TY - JOUR
T1 - Leucine restores murine hepatic triglyceride accumulation induced by a low-protein diet by suppressing autophagy and excessive endoplasmic reticulum stress
AU - Yokota, Shin Ichi
AU - Ando, Midori
AU - Aoyama, Shinya
AU - Nakamura, Kawai
AU - Shibata, Shigenobu
N1 - Funding Information:
This work was partially supported by the Council for Science, Technology and Innovation, SIP, “Technologies for creating next-generation agriculture, forestry and fisheries” (funding agency: Bio-oriented Technology Research Advancement Institution, NARO) (S.S.); by a Grant-in-Aid for Scientific Research (S) (26220201) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan (S.S.); and by a Grant-in-Aid for Scientific Research (C) (15K07740) from the Japan Society for the Promotion of Science (S.Y.). No additional external funding was received for this study.
Publisher Copyright:
© Springer-Verlag Wien 2015.
PY - 2016/4
Y1 - 2016/4
N2 - Although it is known that a low-protein diet induces hepatic triglyceride (TG) accumulation in both rodents and humans, little is known about the underlying mechanism. In the present study, we modeled hepatic TG accumulation by inducing dietary protein deficiency in mice and aimed to determine whether certain amino acids could prevent low-protein diet-induced TG accumulation in the mouse liver. Mice fed a diet consisting of 3 % casein (3C diet) for 7 days showed hepatic TG accumulation with up-regulation of TG synthesis for the Acc gene and down-regulation of TG-rich lipoprotein secretion from hepatocytes for Mttp genes. Supplementing the 3 % casein diet with essential amino acids, branched-chain amino acids, or the single amino acid leucine rescued hepatic TG accumulation. In the livers of mice fed the 3 % casein diet, we observed a decrease in the levels of the autophagy substrate p62, an increase in the expression levels of the autophagy marker LC3-II, and an increase in the splicing of the endoplasmic reticulum (ER) stress-dependent Xbp1 gene. Leucine supplementation to the 3 % casein diet did not affect genes related to lipid metabolism, but inhibited the decrease in p62, the increase in LC3-II, and the increase in Xbp1 splicing levels in the liver. Our results suggest that ER stress responses and activated autophagy play critical roles in low-protein diet-induced hepatic TG accumulation in mice, and that leucine suppresses these two major protein degradation systems. This study contributes to understanding the mechanisms of hepatic disorders of lipid metabolism.
AB - Although it is known that a low-protein diet induces hepatic triglyceride (TG) accumulation in both rodents and humans, little is known about the underlying mechanism. In the present study, we modeled hepatic TG accumulation by inducing dietary protein deficiency in mice and aimed to determine whether certain amino acids could prevent low-protein diet-induced TG accumulation in the mouse liver. Mice fed a diet consisting of 3 % casein (3C diet) for 7 days showed hepatic TG accumulation with up-regulation of TG synthesis for the Acc gene and down-regulation of TG-rich lipoprotein secretion from hepatocytes for Mttp genes. Supplementing the 3 % casein diet with essential amino acids, branched-chain amino acids, or the single amino acid leucine rescued hepatic TG accumulation. In the livers of mice fed the 3 % casein diet, we observed a decrease in the levels of the autophagy substrate p62, an increase in the expression levels of the autophagy marker LC3-II, and an increase in the splicing of the endoplasmic reticulum (ER) stress-dependent Xbp1 gene. Leucine supplementation to the 3 % casein diet did not affect genes related to lipid metabolism, but inhibited the decrease in p62, the increase in LC3-II, and the increase in Xbp1 splicing levels in the liver. Our results suggest that ER stress responses and activated autophagy play critical roles in low-protein diet-induced hepatic TG accumulation in mice, and that leucine suppresses these two major protein degradation systems. This study contributes to understanding the mechanisms of hepatic disorders of lipid metabolism.
KW - Autophagy
KW - ER stress
KW - Fatty liver
KW - Metabolic syndrome
KW - Unfolded protein response
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U2 - 10.1007/s00726-015-2149-0
DO - 10.1007/s00726-015-2149-0
M3 - Article
C2 - 26707165
AN - SCOPUS:84951921398
VL - 48
SP - 1013
EP - 1021
JO - Amino Acids
JF - Amino Acids
SN - 0939-4451
IS - 4
ER -