Project description:The Cytoplasmic Polyadenylation Element Binding (CPEB)-family of RNA-binding proteins regulates pre-mRNA processing and translation of CPE-containing mRNAs in early embryonic development and synaptic activity. However, the specific functions of each CPEB in the adult organism are poorly understood. Here we show that CPEB4 is required to suppress high fat diet- and aging-induced endoplasmic reticulum (ER) stress, and its subsequent hepatic steatosis. Stress-activated expression of CPEB4 in the liver is controlled through a double layer of regulation. First, Cpeb4 is transcriptionally regulated by the circadian clock and then, its mRNA translation is regulated by the Unfolded Protein Response (UPR) through the upstream Open Reading Frames (uORFs) present in its 5’ UTR. Thus, CPEB4 is synthesized only upon ER-stress but the amplitude of the induction is circadian. In turn, CPEB4 activates a second wave of UPR-translation required to maintain ER and mitochondrial homeostasis. Our results suggest that combined transcriptional and translational regulation of CPEB4 generates a “circadian mediator”, which coordinates the hepatic UPR activity with periods of high ER protein-folding demand preventing non-alcoholic fatty liver disease (NAFLD).
Project description:The Cytoplasmic Polyadenylation Element Binding (CPEB)-family of RNA-binding proteins regulates pre-mRNA processing and translation of CPE-containing mRNAs in early embryonic development and synaptic activity. However, the specific functions of each CPEB in the adult organism are poorly understood. Here we show that CPEB4 is required to suppress high fat diet- and aging-induced endoplasmic reticulum (ER) stress, and its subsequent hepatic steatosis. Stress-activated expression of CPEB4 in the liver is controlled through a double layer of regulation. First, Cpeb4 is transcriptionally regulated by the circadian clock and then, its mRNA translation is regulated by the Unfolded Protein Response (UPR) through the upstream Open Reading Frames (uORFs) present in its 5’ UTR. Thus, CPEB4 is synthesized only upon ER-stress but the amplitude of the induction is circadian. In turn, CPEB4 activates a second wave of UPR-translation required to maintain ER and mitochondrial homeostasis. Our results suggest that combined transcriptional and translational regulation of CPEB4 generates a “circadian mediator”, which coordinates the hepatic UPR activity with periods of high ER protein-folding demand preventing non-alcoholic fatty liver disease (NAFLD).
Project description:Background: Ginseng flower bud (GFB) is a part of ginseng with high content of ginsenosides, the known active components of ginseng. While the scientific data for the pharmacological activity of ginseng roots are accumulating, the therapeutic potential of GFB have been neglected. The current study aimed to examine the therapeutic effect of GFB on hepatic steatosis and to elucidate the underlying mechanisms. Methods: HepG2 cells treated with free fatty acids mixture and hepatocytes isolated from rats after 3 weeks of HFD feeding were used as in vitro models of hepatic steatosis for evaluation of anti-steatotic effect of GFB. The effect of GFB was further investigated in pathological conditions of hepatic steatosis induced by 12 weeks of HFD feeding in C57BL/6J mice. We performed systematical analyses on hepatic gene expression profiles in GFB treated mice. The effect of GFB on the expression profile of selected genes was validated by quantitative PCR. Results: GFB treatment markedly reduced oil red O stained lipid droplets and intracellular triglyceride levels in HepG2 cells and rat hepatocytes. In HFD-fed mice, GFB (500 mg/kg) treatment markedly reduced histological signs of hepatic steatosis and decreased hepatic triglyceride content by 34.1% compared to those of HFD. These changes by GFB treatment were accompanied by improved insulin signaling. Global gene expression analysis revealed that hepatic gene expression in the steatotic liver was reversed by GFB treatment, and the GFB-regulated genes are involved in immune process, insulin response and lipid storage. Conclusion: These findings provide a substantial evidence for the medicinal use of GFB in prevention or treatment of NAFLD through suppression of hepatic inflammation and fatty acid uptake while sensitizing hepatic insulin signaling
Project description:Hepatic steatosis is a very common response to liver injury and often attributed to metabolic disorders. Prior studies have demonstrated the efficacy of a biotechnologically produced oyster mushroom (Pleurotus sajor-caju, PSC) in alleviating hepatic steatosis in obese Zucker rats. This study aims to elucidate molecular events underlying the anti-steatotic effects of PSC.
Project description:Erythropoiesis is essential to mammals and is regulated at multiple steps by both extracellular and intracellular factors. Many transcriptional regulatory networks in erythroid differentiation have been well characterized. However, our understanding of post-transcriptional regulatory circuitries in this developmental process is still limited. Using genomic approaches, we identified a sequence-specific RNA-binding protein, Cpeb4, which is dramatically induced in terminal erythroid differentiation (TED) by two erythroid important transcription factors, Gata1/Tal1. Cpeb4 belongs to the cytoplasmic polyadenylation element binding (CPEB) protein family that regulates translation of target mRNAs in early embryonic development, neuronal synapse, and cancer. Using primary mouse fetal liver erythroblasts, we found that Cpeb4 is required for terminal erythropoiesis by repressing the translation of a set of mRNAs highly expressed in progenitor cells. This translational repression occurs by the interaction with a general translational initiation factor, eIF3. Interestingly, Cpeb4 also binds its own mRNA and represses its translation, thus forming a negative regulatory circuitry to limit Cpeb4 protein level. This mechanism ensures that the translation repressor, Cpeb4, does not interfere with the translation of other mRNAs in differentiating erythroblasts. Our study characterized a translational regulatorycircuitry that controls TED and revealed that Cpeb4 is required for somatic cell differentiation. We used microarray to identify mRNAs associated with Cpeb4 in mouse fetal liver erythroblasts. Cpeb4 associated mRNAs were isolated from mouse fetal liver erythroblasts using anti-Cpeb4 antibody for immunoprecipitation followed by RNA extraction. Then Affymetrix microarrays were used to identify and quantify the mRNAs associated with Cpeb4.
Project description:Alcohol’s impairment of both hepatic lipid metabolism and insulin resistance (IR) are key drivers of alcoholic steatosis, the initial stage of alcoholic liver disease (ALD). Pharmacologic reduction of lipotoxic ceramide prevents alcoholic steatosis and glucose intolerance in mice, but potential off-target effects limit its strategic utility. Here, we employed a hepatic-specific acid-ceramidase (ASAH) overexpression model to reduce hepatic ceramides in a Lieber-DeCarli model of experimental alcoholic steatosis. We examined effects of alcohol on hepatic lipid metabolism, body composition, energy homeostasis and insulin sensitivity as measured by hyperinsulinemic-euglycemic clamp. Our results demonstrate that hepatic ceramide reduction ameliorates the effects of alcohol on hepatic lipid droplet accumulation by promoting VLDL secretion and lipophagy, the latter of which involves ceramide cross-talk between the lysosomal and lipid droplet compartments. We additionally demonstrate that hepatic ceramide reduction prevents alcohol’s inhibition of hepatic insulin signaling. These effects on the liver are associated with a reduction in oxidative stress markers and are relevant to humans, as we observe peri-lipid droplet ASAH expression in human ALD. Together, our results suggest a potential role for hepatic ceramide inhibition in preventing ALD.