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Hepatocyte-Specific Depletion of UBXD8 Induces Periportal Steatosis in Mice Fed a High-Fat Diet.

Imai N, Suzuki M, Hayashi K, Ishigami M, Hirooka Y, Abe T, Shioi G, Goto H, Fujimoto T - PLoS ONE (2015)

Bottom Line: We showed previously that UBXD8 plays a key role in proteasomal degradation of lipidated ApoB in hepatocarcinoma cell lines.The decrease of ApoB secretion upon UBXD8 depletion was recapitulated in cultured primary hepatocytes.Accumulation of lipidated ApoB in lipid droplets was observed only in UBXD8- hepatocytes.

View Article: PubMed Central - PubMed

Affiliation: Department of Anatomy and Molecular Cell Biology, Nagoya University Graduate School of Medicine, Nagoya, Japan; Department of Gastroenterology and Hepatology, Nagoya University Graduate School of Medicine, Nagoya, Japan.

ABSTRACT
We showed previously that UBXD8 plays a key role in proteasomal degradation of lipidated ApoB in hepatocarcinoma cell lines. In the present study, we aimed to investigate the functions of UBXD8 in liver in vivo. For this purpose, hepatocyte-specific UBXD8 knockout (UBXD8-LKO) mice were generated. They were fed with a normal or high-fat diet, and the phenotypes were compared with those of littermate control mice. Hepatocytes obtained from UBXD8-LKO and control mice were analyzed in culture. After 26 wk of a high-fat diet, UBXD8-LKO mice exhibited macrovesicular steatosis in the periportal area and microvesicular steatosis in the perivenular area, whereas control mice exhibited steatosis only in the perivenular area. Furthermore, UBXD8-LKO mice on a high-fat diet had significantly lower concentrations of serum triglyceride and VLDL than control mice. A Triton WR-1339 injection study revealed that VLDL secretion from hepatocytes was reduced in UBXD8-LKO mice. The decrease of ApoB secretion upon UBXD8 depletion was recapitulated in cultured primary hepatocytes. Accumulation of lipidated ApoB in lipid droplets was observed only in UBXD8- hepatocytes. The results showed that depletion of UBXD8 in hepatocytes suppresses VLDL secretion, and could lead to periportal steatosis when mice are fed a high-fat diet. This is the first demonstration that an abnormality in the intracellular ApoB degradation mechanism can cause steatosis, and provides a useful model for periportal steatosis, which occurs in several human diseases.

No MeSH data available.


Related in: MedlinePlus

Analysis of serum lipoproteins.(A) Lipoprotein profile obtained by gel filtration–HPLC of mouse serum at 30 wk old. A representative result on TG (blue) and total cholesterol (red) is shown for sera of normal and UBXD8-LKO male mice fed a normal (A) or a high-fat diet (B). Sera from female mice gave similar results. Sera for the UBXD8-LKO group fed a high-fat diet were taken from mice showing periportal steatosis. Lower panels show a magnified view of the VLDL portion. FG: free glycerol. (B) VLDL-TG was lower in UBXD8-LKO mice than in normal mice, even when they were fed a normal diet. The difference between the control and UBXD8-LKO mouse became significantly larger when mice were fed a high-fat diet. P values were obtained by non-paired Student's t test (n = 3; means ± SEM). (C) The TG-to-cholesterol ratio in VLDL tended to be lower in the UBXD8-LKO than in the control mouse. P values were obtained by non-paired Student's t test (n = 3; means ± SEM).
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pone.0127114.g005: Analysis of serum lipoproteins.(A) Lipoprotein profile obtained by gel filtration–HPLC of mouse serum at 30 wk old. A representative result on TG (blue) and total cholesterol (red) is shown for sera of normal and UBXD8-LKO male mice fed a normal (A) or a high-fat diet (B). Sera from female mice gave similar results. Sera for the UBXD8-LKO group fed a high-fat diet were taken from mice showing periportal steatosis. Lower panels show a magnified view of the VLDL portion. FG: free glycerol. (B) VLDL-TG was lower in UBXD8-LKO mice than in normal mice, even when they were fed a normal diet. The difference between the control and UBXD8-LKO mouse became significantly larger when mice were fed a high-fat diet. P values were obtained by non-paired Student's t test (n = 3; means ± SEM). (C) The TG-to-cholesterol ratio in VLDL tended to be lower in the UBXD8-LKO than in the control mouse. P values were obtained by non-paired Student's t test (n = 3; means ± SEM).

Mentions: In light of the finding that the serum TG level was significantly lower in UBXD8-LKO mice than controls under a high-fat diet, we analyzed the lipoprotein profile to measure TG in lipoprotein fractions (Fig 5A). TG in VLDL (VLDL-TG) was lower in UBXD8-LKO mice than in controls, and the difference became significantly larger when the animals were fed a high-fat diet (Fig 5B). The TG-to-cholesterol ratio in VLDL was also lower in UBXD8-LKO mice than in controls whether mice were fed a normal or a high-fat diet (Fig 5C). Considering that TG and cholesterol are largely present in the core and the outer phospholipid monolayer of the VLDL particle, respectively, these results suggested that lipidation of ApoB (i.e., loading of TG to nascent ApoB) is defective in the UBXD8- hepatocytes.


Hepatocyte-Specific Depletion of UBXD8 Induces Periportal Steatosis in Mice Fed a High-Fat Diet.

Imai N, Suzuki M, Hayashi K, Ishigami M, Hirooka Y, Abe T, Shioi G, Goto H, Fujimoto T - PLoS ONE (2015)

Analysis of serum lipoproteins.(A) Lipoprotein profile obtained by gel filtration–HPLC of mouse serum at 30 wk old. A representative result on TG (blue) and total cholesterol (red) is shown for sera of normal and UBXD8-LKO male mice fed a normal (A) or a high-fat diet (B). Sera from female mice gave similar results. Sera for the UBXD8-LKO group fed a high-fat diet were taken from mice showing periportal steatosis. Lower panels show a magnified view of the VLDL portion. FG: free glycerol. (B) VLDL-TG was lower in UBXD8-LKO mice than in normal mice, even when they were fed a normal diet. The difference between the control and UBXD8-LKO mouse became significantly larger when mice were fed a high-fat diet. P values were obtained by non-paired Student's t test (n = 3; means ± SEM). (C) The TG-to-cholesterol ratio in VLDL tended to be lower in the UBXD8-LKO than in the control mouse. P values were obtained by non-paired Student's t test (n = 3; means ± SEM).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4430229&req=5

pone.0127114.g005: Analysis of serum lipoproteins.(A) Lipoprotein profile obtained by gel filtration–HPLC of mouse serum at 30 wk old. A representative result on TG (blue) and total cholesterol (red) is shown for sera of normal and UBXD8-LKO male mice fed a normal (A) or a high-fat diet (B). Sera from female mice gave similar results. Sera for the UBXD8-LKO group fed a high-fat diet were taken from mice showing periportal steatosis. Lower panels show a magnified view of the VLDL portion. FG: free glycerol. (B) VLDL-TG was lower in UBXD8-LKO mice than in normal mice, even when they were fed a normal diet. The difference between the control and UBXD8-LKO mouse became significantly larger when mice were fed a high-fat diet. P values were obtained by non-paired Student's t test (n = 3; means ± SEM). (C) The TG-to-cholesterol ratio in VLDL tended to be lower in the UBXD8-LKO than in the control mouse. P values were obtained by non-paired Student's t test (n = 3; means ± SEM).
Mentions: In light of the finding that the serum TG level was significantly lower in UBXD8-LKO mice than controls under a high-fat diet, we analyzed the lipoprotein profile to measure TG in lipoprotein fractions (Fig 5A). TG in VLDL (VLDL-TG) was lower in UBXD8-LKO mice than in controls, and the difference became significantly larger when the animals were fed a high-fat diet (Fig 5B). The TG-to-cholesterol ratio in VLDL was also lower in UBXD8-LKO mice than in controls whether mice were fed a normal or a high-fat diet (Fig 5C). Considering that TG and cholesterol are largely present in the core and the outer phospholipid monolayer of the VLDL particle, respectively, these results suggested that lipidation of ApoB (i.e., loading of TG to nascent ApoB) is defective in the UBXD8- hepatocytes.

Bottom Line: We showed previously that UBXD8 plays a key role in proteasomal degradation of lipidated ApoB in hepatocarcinoma cell lines.The decrease of ApoB secretion upon UBXD8 depletion was recapitulated in cultured primary hepatocytes.Accumulation of lipidated ApoB in lipid droplets was observed only in UBXD8- hepatocytes.

View Article: PubMed Central - PubMed

Affiliation: Department of Anatomy and Molecular Cell Biology, Nagoya University Graduate School of Medicine, Nagoya, Japan; Department of Gastroenterology and Hepatology, Nagoya University Graduate School of Medicine, Nagoya, Japan.

ABSTRACT
We showed previously that UBXD8 plays a key role in proteasomal degradation of lipidated ApoB in hepatocarcinoma cell lines. In the present study, we aimed to investigate the functions of UBXD8 in liver in vivo. For this purpose, hepatocyte-specific UBXD8 knockout (UBXD8-LKO) mice were generated. They were fed with a normal or high-fat diet, and the phenotypes were compared with those of littermate control mice. Hepatocytes obtained from UBXD8-LKO and control mice were analyzed in culture. After 26 wk of a high-fat diet, UBXD8-LKO mice exhibited macrovesicular steatosis in the periportal area and microvesicular steatosis in the perivenular area, whereas control mice exhibited steatosis only in the perivenular area. Furthermore, UBXD8-LKO mice on a high-fat diet had significantly lower concentrations of serum triglyceride and VLDL than control mice. A Triton WR-1339 injection study revealed that VLDL secretion from hepatocytes was reduced in UBXD8-LKO mice. The decrease of ApoB secretion upon UBXD8 depletion was recapitulated in cultured primary hepatocytes. Accumulation of lipidated ApoB in lipid droplets was observed only in UBXD8- hepatocytes. The results showed that depletion of UBXD8 in hepatocytes suppresses VLDL secretion, and could lead to periportal steatosis when mice are fed a high-fat diet. This is the first demonstration that an abnormality in the intracellular ApoB degradation mechanism can cause steatosis, and provides a useful model for periportal steatosis, which occurs in several human diseases.

No MeSH data available.


Related in: MedlinePlus