Yuki Mori, Masashi Masuda, Risa Yoshida-Shimizu, Saki Aoyagi, Yuichiro Adachi, The Anh Nguyen, Yusuke Maruyama, Yosuke Okumura, Yuki Kamei, Maiko Sakai, Kohta Ohnishi, Hirokazu Ohminami and Yutaka Taketani : All-trans retinoic acid induces lipophagy through the activation of the AMPK-Beclin1 signaling pathway and reduces Rubicon expression in adipocytes., The Journal of Nutritional Biochemistry, Vol.126, 2024.
(Summary)
Lipophagy is defined as a lipolysis pathway that degrades lipid droplet (LD) via autophagy. All-trans retinoic acid (atRA), a metabolite of vitamin A, stimulates lipolysis through hormone-sensitive lipase and β-oxidation. However, the regulation of lipolysis by atRA-induced autophagy in adipocytes remains unclear. In this study, we investigated the effect of atRA on autophagy in epididymal fat of mice and the molecular mechanisms of autophagy in 3T3-L1 adipocytes. Western blotting showed that atRA decreased the expression of p62, a cargo receptor for autophagic degradation, and increased the expression of the lipidated LC3B (LC3B-II), an autophagy marker, in epididymal fat. Next, we confirmed that atRA increased autophagic flux in differentiated 3T3-L1 cells using the GFP-LC3-RFP-LC3ΔG probe. Immunofluorescent staining revealed that the colocalization of LC3B with perilipin increased in differentiated 3T3-L1 cells treated with atRA. The knockdown of Atg5, an essential gene in autophagy induction, partly suppressed the atRA-induced release of non-esterified fatty acid (NEFA) from LDs in differentiated 3T3-L1 cells. atRA time-dependently elicited the phosphorylation of AMPK and Beclin1, autophagy-inducing factors, in mature 3T3-L1 adipocytes. Inversely, atRA decreased the protein expression of Rubicon, an autophagy repressor, in differentiated 3T3-L1 cells and epididymal fat. Interestingly, the expression of ALDH1A1, atRA-synthesizing enzymes, increased in epididymal fat with decreased protein expression of Rubicon in aged mice. These results suggest that atRA may partially induce lipolysis through lipophagy by activating the AMPK-Beclin1 signaling pathway in the adipocytes and increased atRA levels may contribute to decreased Rubicon expression in the epididymal fat of aged mice. (248/250 words).
Yuki Kamei, Yosuke Okumura, Yuichiro Adachi, Yuki Mori, Maiko Sakai, Kohta Ohnishi, Hirokazu Ohminami, Masashi Masuda, Hisami Yamanaka-Okumura and Yutaka Taketani : Humoral and cellular factors inhibit phosphate-induced vascular calcification during the growth period., Journal of Clinical Biochemistry and Nutrition, Vol.73, No.3, 198-204, 2023.
(Summary)
, obvious calcification was observed in the adult aorta but not in the young aorta. Furthermore, culture in high Pi medium increased the mRNA level of tissue-nonspecific alkaline phosphatase (TNAP), which degrades pyrophosphate, only in the adult aorta. Collectively, our findings indicate that the aorta in growing mouse may be resistant to Pi-induced vascular calcification via a mechanism in which high serum fetuin-A levels and suppressed TNAP expression.
Vascular calcification is an important pathogenesis related to cardiovascular disease and high mortality rate in chronic kidney disease (CKD) patients. It has been well-known that hyper-phosphatemia induces osteochondrogenic transition of vascular smooth muscle cells (VSMCs) resulting ectopic calcification in aortic media, cardiac valve, and kidney. However, the detailed mechanism of the ectopic calcification has been not clarified yet. Here, we found that the co-localization of CYP27B1 with the calcified lesions of aorta and arteries in kidney of klotho mutant () mice, and then investigated the role of CYP27B1 in the mineralization of the VSMCs. Under high phosphate condition, overexpression of CYP27B1 induced calcification and osteocalcin mRNA expression in the VSMCs. Inversely, siRNA- inhibited high phosphate-induced calcification of the VSMCs. We also found that the accumulated CYP27B1 protein was glycosylated in the kidney of mice. Therefore, overexpression of CYP27B1-N310A and CYP27B1-T439A, which are a mutation for -linked glycosylation site (N310A) and a mutation for -linked glycosylation site (T439A) in CYP27B1, decreased calcium deposition and expression of RUNX2 induced by high phosphate medium in VSMCs compared with wild-type CYP27B1. These results suggest that extra-renal expression of glycosylated CYP27B1 would be required for ectopic calcification of VSMCs under hyperphosphatemia.
Yuichiro Adachi, Masashi Masuda, Iori Sakakibara, Takayuki Uchida, Yuki Niida, Yuki Mori, Yuki Kamei, Yosuke Okumura, Hirokazu Ohminami, Kohta Ohnishi, Hisami Okumura, Takeshi Nikawa and Yutaka Taketani : All-trans retinoic acid changes muscle fiber type via increasing GADD34 dependent on MAPK signal., Life Science Alliance, Vol.5, No.7, 2022.
(Summary)
All-trans retinoic acid (ATRA) increases the sensitivity to unfolded protein response in differentiating leukemic blasts. The downstream transcriptional factor of PERK, a major arm of unfolded protein response, regulates muscle differentiation. However, the role of growth arrest and DNA damage-inducible protein 34 (GADD34), one of the downstream factors of PERK, and the effects of ATRA on GADD34 expression in muscle remain unclear. In this study, we identified ATRA increased the GADD34 expression independent of the PERK signal in the gastrocnemius muscle of mice. ATRA up-regulated GADD34 expression through the transcriptional activation of gene via inhibiting the interaction of homeobox Six1 and transcription co-repressor TLE3 with the MEF3-binding site on the gene promoter in skeletal muscle. ATRA also inhibited the interaction of TTP, which induces mRNA degradation, with AU-rich element on mRNA via p-38 MAPK, resulting in the instability of mRNA. Overexpressed GADD34 in C2C12 cells changes the type of myosin heavy chain in myotubes. These results suggest ATRA increases GADD34 expression via transcriptional and post-transcriptional regulation, which changes muscle fiber type.
Yuki Kamei, Okumura Yosuke, Adachi Yuichiro, mori Yuki, Hirokazu Ohminami, Masashi Masuda and Yutaka Taketani : Inhibitory Mechanism of Ectopic Calcification during Growth Period, The American Society for Bone and Mineral Research 2022 Annual Meeting, Online, Sep. 2022.