Hepatocyte Kctd17 Inhibition Ameliorates Glucose Intolerance and Hepatic Steatosis Caused by Obesity-induced Chrebp Stabilization.
Obesity predisposes to type 2 diabetes (T2D) and nonalcoholic fatty liver disease (NAFLD), but underlying mechanisms are incompletely understood. Potassium channel tetramerization domain-containing protein 17 (Kctd17) levels are increased in livers from obese mice and humans. In this study, we investigated the mechanism of increased Kctd17 and whether it is causal to obesity-induced metabolic complications.
We transduced Rosa26-LSL-Cas9 knockin mice with AAV8-TBG-Cre (Control), AAV8-U6-Kctd17 sgRNA-TBG-Cre (L-Kctd17), AAV8-U6-Oga sgRNA-TBG-Cre (L-Oga), or AAV8-U6-Kctd17/Oga sgRNA-TBG-Cre (DKO). We fed mice a high-fat diet (HFD) and assessed for hepatic glucose and lipid homeostasis. We generated Kctd17, O-GlcNAcase (Oga), or Kctd17/Oga-knockout hepatoma cells by CRISPR-Cas9, and Kctd17-directed antisense oligonucleotide to test therapeutic potential in vivo. We analyzed transcriptomic data from patients with NAFLD.
Hepatocyte Kctd17 expression was increased in HFD-fed mice due to increased Srebp1c activity. HFD-fed L-Kctd17 or Kctd17 antisense oligonucleotide-treated mice show improved glucose tolerance and hepatic steatosis, whereas forced Kctd17 expression caused glucose intolerance and hepatic steatosis even in lean mice. Kctd17 induced Oga degradation, resulting in increasing carbohydrate response element-binding protein (Chrebp) protein, so concomitant Oga knockout negated metabolic benefits of hepatocyte Kctd17 deletion. In patients with NAFLD, KCTD17 messenger RNA was positively correlated with expression of Chrebp target and other lipogenic genes.
Srebp1c-induced hepatocyte Kctd17 expression in obesity disrupted glucose and lipid metabolism by stabilizing Chrebp, and may represent a novel therapeutic target for obesity-induced T2D and NAFLD.
Oh AR
，Jeong Y
，Yu J
，Minh Tam DT
，Kang JK
，Jung YH
，Im SS
，Lee SB
，Ryu D
，Pajvani UB
，Kim K
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Gracilaria chorda subcritical water ameliorates hepatic lipid accumulation and regulates glucose homeostasis in a hepatic steatosis cell model and obese C57BL/6J mice.
Red seaweed, known as Rhodophyta, has a long history of use in traditional Asian medicine, including Traditional Chinese Medicine and Ayurveda. It is believed to have cooling and detoxification properties. Red seaweed species, such as Gracilaria, have been used in traditional remedies to address various conditions, such as inflammation, thyroid disorders, and digestive issues.
Obesity is a risk factor of hepatic steatosis, a hallmark of non-alcoholic fatty liver disease (NAFLD) that affects nearly 25% of the worldwide population. Gracilaria chorda (GC) contains bioactive peptides that may be applicable in the prevention of metabolic syndrome diseases. This study investigated the effects of GC subcritical water extract at 210 °C (GCSW210) on preventing liver injury and lipid and glucose dysregulation in an oleic acid (OA)-induced hepatic steatosis cell model (HepG2) and high-fat diet (HFD)-induced obese animal model (C57BL/6J mice).
Human hepatoma HepG2 cells were exposed to 0.1 mM OA for 24 h to induce hepatic steatosis and C57BL/6J mice were fed a HFD for 13 weeks. For lipid accumulation, triglyceride (TG) content was measured in both models, along with free fatty acid (FFA), plasma glucose, and insulin levels in HFD-fed mice. Protein expression of master regulators of adipogenesis and lipogenesis, as well as cholesterol and mitochondrial biosynthesis, was studied via western blotting in hepatic steatosis-induced in vitro and in vivo models. In addition, protein expression of the insulin signaling cascade in skeletal muscle tissues of HFD-fed mice was studied.
GCSW210 significantly decreased lipid accumulation in HepG2 cells exposed to OA and suppressed the expression of lipogenic factors, such as sterol regulatory element-binding protein (SREBP)-1c and fatty acid synthase. In addition, GCSW210 abrogated transcription factors related to cholesterol biosynthesis, such as SREBP-2 and low-density lipoprotein receptor. Similarly, FFA, TG, serum glutamic acid, aspartate transaminase, alanine transferase, plasma glucose, and insulin levels were also significantly reduced in GCSW210-treated HFD-fed mice, which were comparable to the positive control mice treated with Garcinia cambogia extract. Additionally, GCSW210 enhanced the phosphorylation of AMP-activated protein kinase (AMPK) and acetyl-CoA carboxylase in the hepatic tissues of HFD-fed mice. Moreover, GCSW210 treatment improved insulin signal transduction by reducing insulin receptor substrate 1 Ser307 phosphorylation and elevated phosphatidylinositol 3-kinase/protein kinase B and glucose transporter type 4 protein expression in muscle tissue. 5-Hdroxymethylfufural (5-HMF) was confirmed to be active substances isolated from GCSW210 through LC-PDA and LC-MS.
GCSW210 significantly regulated glucose metabolism, alleviated insulin resistance (IR) induced by high fatty acid synthesis and lipid accumulation, and elevated de novo lipogenesis by activating AMPK phosphorylation in both the liver and muscle tissues of HFD-fed mice. GCSW210 may be a potential functional food for preventing HFD-induced metabolic diseases, such as IR, NAFLD, and type 2 diabetes mellitus.
Thakuri LS
，Park CM
，Kim HA
，Kim HJ
，Park JW
，Park JC
，Rhyu DY
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N(6) -Methyladenosine Reader Protein YT521-B Homology Domain-Containing 2 Suppresses Liver Steatosis by Regulation of mRNA Stability of Lipogenic Genes.
Nonalcoholic fatty liver disease (NAFLD) is characterized by accumulation of excessive triglycerides (TGs) in hepatocytes. Obesity is a major risk factor for developing fatty liver, although the intracellular molecular basis remains largely unclear. N6 -methyladenosine (m6 A) RNA methylation is the most common internal modification in eukaryotic mRNA.
In the present study, by m6 A sequencing and RNA sequencing, we found that both m6 A enrichment and mRNA expression of lipogenic genes were significantly increased in leptin-receptor-deficient db/db mice. Importantly, our results showed that YT521-B homology domain-containing 2 (Ythdc2), an m6 A reader, was markedly down-regulated in livers of obese mice and NAFLD patients. Suppression of Ythdc2 in livers of lean mice led to TG accumulation, whereas ectopic overexpression of Ythdc2 in livers of obese mice improved liver steatosis and insulin resistance. Mechanistically, we found that Ythdc2 could bind to mRNA of lipogenic genes, including sterol regulatory element-binding protein 1c, fatty acid synthase, stearoyl-CoA desaturase 1, and acetyl-CoA carboxylase 1, to decrease their mRNA stability and inhibit gene expression.
Our findings describe an important role of the m6 A reader, Ythdc2, for regulation of hepatic lipogenesis and TG homeostasis, which might provide a potential target for treating obesity-related NAFLD.
Zhou B
，Liu C
，Xu L
，Yuan Y
，Zhao J
，Zhao W
，Chen Y
，Qiu J
，Meng M
，Zheng Y
，Wang D
，Gao X
，Li X
，Zhao Q
，Wei X
，Wu D
，Zhang H
，Hu C
，Zhuo X
，Zheng M
，Wang H
，Lu Y
，Ma X
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