Changes In Hepatic Lipid Metabolism Research Articles

Seasonal changes in hepatic lipid metabolism and apoptosis in Chinese soft-shelled turtle (Pelodiscus sinensis)

Chinese soft-shelled turtle (Pelodiscus sinensis) hibernates without eating and drinking when the ambient temperature is very low. To better understand the characteristics of energy utilization during hibernation, the turtles in the physiological phases of summer active (SA), Pre-Hibernation (Pre-H), Mid-Hibernation (Mid-H) and early arousal (EA) were sampled. The results showed that the levels of serum triglyceride and hepatic lipid droplet were markedly increased in Pre-H and decreased in Mid-H compared with that in SA, indicating that P. sinensis experiences lipid accumulation in Pre-H and lipid is the predominant energy reserve during hibernation. The mRNA expression levels of genes (FABP and CPT-2) involved in lipolysis and lipid oxidation were up-regulated in Mid-H, while the genes related to lipid synthesis (FAS, ACSL-1, ACC, elovl5, and SCD1) were inhibited in Mid-H. Meanwhile, the mRNA expression levels of endoplasmic reticulum stress marker gene Bip and key genes (ATF4, ATF6, and IRE1α) involving the unfolded protein response were significantly increased in Mid-H and EA. Also, the expression levels of genes (ASK1, JNK1, and Bax) associated with cell apoptosis increased in Mid-H and EA, however, the expression of Bcl2 was inhibited in Mid-H. Therefore, hibernation can cause endoplasmic reticulum stress and apoptosis. The findings will provide a theoretical framework for an animal's cold adaptation and offer insights into preventing and managing metabolic syndrome.

Age-Related Changes in Hepatic Lipid Metabolism and Abdominal Adipose Deposition in Yellow-Feathered Broilers Aged from 1 to 56 Days.

The objective of this study was to evaluate the age-related changes in hepatic lipid metabolism, adipocyte hyperplasia, hypertrophy, and lipid metabolism in the abdominal adipose tissue of yellow-feathered broilers. Blood, liver, and abdominal adipose samples were collected on days 1, 7, 14, 21, 28, 35, 42, 49, and 56. Body, liver, and abdominal weight increased (p < 0.05) with age-related changes. The triacylglycerol content peaked on day 14, and total cholesterol content peaked on day 56. The adipocyte diameter and area peaked on day 56, and total DNA content peaked on day 7. The age-related changes in hepatic lipogenesis-related gene (ChREBP, SREBP-1c, ACC, FAS, SCD1) expression mainly occurred during days 1 to 21, hepatic lipolysis-related gene (CPT1, LPL, ApoB) expression mainly occurred during days 1 to 14, and abdominal adipose-deposition-related gene (PPARα, CPT1, LPL, PPARγ, C/EBPβ) expression occurred during days 1 to 14. These results demonstrated a dynamic pattern of hepatic lipid metabolism and abdominal adipose deposition in yellow-feathered broilers, which provides practical strategies to regulate hepatic lipid metabolism and reduce abdominal adipose deposition in yellow-feathered broilers.

MiR-20a-5p targeting mfn2-mediated mitochondria-lipid droplet contacts regulated differential changes in hepatic lipid metabolism induced by two Mn sources in yellow catfish

Understanding the hazards of different forms of metal elements provided innovative insights into their toxicity and environmental risk assessment. To date, few studies had been conducted to investigate the differential effects and mechanisms of MnO2 NPs and MnSO4, two widely distributed environmental pollutants, on hepatic toxicity and lipid metabolism since lipid metabolism-relevant parameters were broadly used as biomarkers for risk assessment of hazardous contaminants. Thus, using yellow catfish Pelteobagrus fulvidraco, an ecologically and economically important freshwater fish as the model, the present study investigated the differential effects and mechanisms of MnO2 NPs and MnSO4 influencing hepatic lipid metabolism. Compared to MnSO4, MnO2 NPs increased hepatic Mn content, induced lipotoxicity, up-regulated the mRNA expression of lipogenic genes, increased peridroplet mitochondrial (PDM) contents, intensified the contact between mitochondria and lipid droplets (LDs), and downregulated miR-20a-5p abundance. Importantly, miR-20a-5p targeted mfn2, which mediated the contact between mitochondria and LDs and influenced changes in lipid metabolism induced by MnO2 NPs. Mechanistically, the direct Mfn2-Plin2 binding and Mfn2 GTPase activity promoted the MnO2 NPs-induced interactions between mitochondria and LDs, which in turn influenced MnO2 NPs-induced changes in hepatic lipid metabolism. For the first time, our findings indicated the significant differences between the changes in body metabolism induced by nanoparticles and inorganic elements, which helped to illuminate different mechanisms governing the responses of aquatic vertebrates to hazardous metal pollutants (MnO2 NPs and MnSO4).

Dietary Nε-(carboxymethyl)lysine is a trigger of non-alcoholic fatty liver disease under high-fat consumption.

The irreversible glycation of proteins produces advanced glycation end products (AGEs) which are triggered to bind the receptor for AGE (RAGE), thereby activating mitogen-activated protein kinase/nuclear factor-κB signaling pathway and stimulating proinflammatory cytokines, ultimately leading to chronic disorders. In this study, we focus the promoting effect of Nε-carboxymethyl-lysine (CML), one of the most dietary AGEs, on non-alcoholic fatty liver disease (NAFLD) and evaluated NAFLD-related biomarkers. Oxidative stress and hepatic steatosis were assessed in oleic acid (OA)-induced HepG2 cells. Using OA-induced HepG2 cells, we show that CML results in oxidative stress and steatosis and drives major changes in hepatic lipid metabolism. Administration of CML exacerbated NAFLD-related symptoms by increasing body and liver weight gain, serum alanine aminotransferase and lipid levels, and insulin resistance in mild high-fat diet-induced mice. Moreover, hepatic histological analysis data, such as staining, western blotting, and RNA-seq, indicate that CML aggravates NAFLD in association with activation of the de novo lipogenesis pathway, consistent with the in vitro assays. Our findings could contribute to model studies related to the prevention and treatment of NAFLD progression due to excessive consumption of dietary AGEs.

The Absence of STING Ameliorates Non-Alcoholic Fatty Liver Disease and Reforms Gut Bacterial Community.

Non-alcoholic fatty liver disease (NAFLD) is one of the primary causes of cirrhosis and a major risk factor for hepatocellular carcinoma and liver-related death. It has been correlated with changes in the gut microbiota, which promote its development by regulating insulin resistance, bile acid and choline metabolism, and inflammation. Recent studies suggested a controversial role of the stimulator of interferon genes (STING) in the development of NAFLD. Here, we showed that as an immune regulator, STING aggravates the progression of NAFLD in diet-induced mice and correlated it with the changes in hepatic lipid metabolism and gut microbiota diversity. After feeding wild-type (WT) and STING deletion mice with a normal control diet (NCD) or a high-fat diet (HFD), the STING deletion mice showed decreased lipid accumulation and liver inflammation compared with WT mice fed the same diet. In addition, STING specifically produced this hepatoprotective effect by inhibiting the activation of CD8+ T cells. The gut microbiota analysis revealed significant differences in intestinal bacteria between STING deletion mice and WT mice under the same diet and environmental conditions; moreover, differential bacterial genera were associated with altered metabolic phenotypes and involved in related metabolic pathways. Overall, our findings reveal the important regulatory role that STING plays in the progression of NAFLD. In addition, the change in intestinal microbiota diversity may be the contributing factor.

Mice with a deficiency in Peroxisomal Membrane Protein 4 (PXMP4) display mild changes in hepatic lipid metabolism

Peroxisomes play an important role in the metabolism of a variety of biomolecules, including lipids and bile acids. Peroxisomal Membrane Protein 4 (PXMP4) is a ubiquitously expressed peroxisomal membrane protein that is transcriptionally regulated by peroxisome proliferator-activated receptor α (PPARα), but its function is still unknown. To investigate the physiological function of PXMP4, we generated a Pxmp4 knockout (Pxmp4−/−) mouse model using CRISPR/Cas9-mediated gene editing. Peroxisome function was studied under standard chow-fed conditions and after stimulation of peroxisomal activity using the PPARα ligand fenofibrate or by using phytol, a metabolite of chlorophyll that undergoes peroxisomal oxidation. Pxmp4−/− mice were viable, fertile, and displayed no changes in peroxisome numbers or morphology under standard conditions. Also, no differences were observed in the plasma levels of products from major peroxisomal pathways, including very long-chain fatty acids (VLCFAs), bile acids (BAs), and BA intermediates di- and trihydroxycholestanoic acid. Although elevated levels of the phytol metabolites phytanic and pristanic acid in Pxmp4−/− mice pointed towards an impairment in peroxisomal α-oxidation capacity, treatment of Pxmp4−/− mice with a phytol-enriched diet did not further increase phytanic/pristanic acid levels. Finally, lipidomic analysis revealed that loss of Pxmp4 decreased hepatic levels of the alkyldiacylglycerol class of neutral ether lipids, particularly those containing polyunsaturated fatty acids. Together, our data show that while PXMP4 is not critical for overall peroxisome function under the conditions tested, it may have a role in the metabolism of (ether)lipids.

Perturbation of TM6SF2 Expression Alters Lipid Metabolism in a Human Liver Cell Line.

Non-alcoholic fatty liver disease (NAFLD) is caused by excess lipid accumulation in hepatocytes. Genome-wide association studies have identified a strong association of NAFLD with non-synonymous E167K amino acid mutation in the transmembrane 6 superfamily member 2 (TM6SF2) protein. The E167K mutation reduces TM6SF2 stability, and its carriers display increased hepatic lipids and lower serum triglycerides. However, the effects of TM6SF2 on hepatic lipid metabolism are not completely understood. We overexpressed wild-type or E167K variant of TM6SF2 or knocked down TM6SF2 expression in lipid-treated Huh-7 cells and used untargeted lipidomic analysis, RNAseq transcriptome analysis, and fluorescent imaging to determine changes in hepatic lipid metabolism. Both TM6SF2 knockdown and E167K overexpression increased hepatic lipid accumulation, while wild-type overexpression decreased acylglyceride levels. We also observed lipid chain remodeling for acylglycerides by TM6SF2 knockdown, leading to a relative increase in species with shorter, more saturated side chains. RNA-sequencing revealed differential expression of several lipid metabolizing genes, including genes belonging to AKR1 family and lipases, primarily in cells with TM6SF2 knockdown. Taken together, our data show that overexpression of TM6SF2 gene or its loss-of-function changes hepatic lipid species composition and expression of lipid metabolizing genes. Additionally, our data further confirms a loss-of-function effect for the E167K variant.

Maternal Exercise Mediates Hepatic Metabolic Programming via Activation of AMPK-PGC1α Axis in the Offspring of Obese Mothers.

Maternal obesity is associated with an increased risk of hepatic metabolic dysfunction for both mother and offspring and targeted interventions to address this growing metabolic disease burden are urgently needed. This study investigates whether maternal exercise (ME) could reverse the detrimental effects of hepatic metabolic dysfunction in obese dams and their offspring while focusing on the AMP-activated protein kinase (AMPK), representing a key regulator of hepatic metabolism. In a mouse model of maternal western-style-diet (WSD)-induced obesity, we established an exercise intervention of voluntary wheel-running before and during pregnancy and analyzed its effects on hepatic energy metabolism during developmental organ programming. ME prevented WSD-induced hepatic steatosis in obese dams by alterations of key hepatic metabolic processes, including activation of hepatic ß-oxidation and inhibition of lipogenesis following increased AMPK and peroxisome-proliferator-activated-receptor-γ-coactivator-1α (PGC-1α)-signaling. Offspring of exercised dams exhibited a comparable hepatic metabolic signature to their mothers with increased AMPK-PGC1α-activity and beneficial changes in hepatic lipid metabolism and were protected from WSD-induced adipose tissue accumulation and hepatic steatosis in later life. In conclusion, this study demonstrates that ME provides a promising strategy to improve the metabolic health of both obese mothers and their offspring and highlights AMPK as a potential metabolic target for therapeutic interventions.

A New Strain of Christensenella minuta as a Potential Biotherapy for Obesity and Associated Metabolic Diseases.

Obesity is associated with gut microbiota dysbiosis, characterized by a high Firmicutes/Bacteroidetes ratio. Gut-dwelling bacteria of the Christensenellaceae family have been proposed to act as keystones of the human gut ecosystem and to prevent adipogenesis. The objectives of the present study were to demonstrate the antiobesity potential of a new strain of Christensenella minuta in preclinical models and explore related mechanisms of action. The antiobesity potential of C. minuta DSM33407 was assessed in a diet-induced obesity mouse model. Changes in hepatic lipid metabolism were explored using targeted transcriptomics. Effects on gut microbiota were further assessed in a humanized Simulator of the Human Intestinal Microbial Ecosystem (SHIME®) model inoculated with obese fecal samples. Shotgun metagenomics was applied to study microbial community structures in both models. C. minuta DSM33407 protected from diet-induced obesity and regulated associated metabolic markers such as glycemia and leptin. It also regulated hepatic lipid metabolism through a strong inhibition of de novo lipogenesis and maintained gut epithelial integrity. In the humanized SHIME® model, these effects were associated with modulations of the intestinal microbiota characterized by a decreased Firmicutes/Bacteroidetes ratio. These data indicate that C. minuta DSM33407 is a convincing therapeutic candidate for the management of obesity and associated metabolic disorders.

Multifaceted Interaction Between Hepatitis B Virus Infection and Lipid Metabolism in Hepatocytes: A Potential Target of Antiviral Therapy for Chronic Hepatitis B.

Hepatitis B virus (HBV) is considered a “metabolic virus” and affects many hepatic metabolic pathways. However, how HBV affects lipid metabolism in hepatocytes remains uncertain yet. Accumulating clinical studies suggested that compared to non-HBV-infected controls, chronic HBV infection was associated with lower levels of serum total cholesterol and triglycerides and a lower prevalence of hepatic steatosis. In patients with chronic HBV infection, high ALT level, high body mass index, male gender, or old age was found to be positively correlated with hepatic steatosis. Furthermore, mechanisms of how HBV infection affected hepatic lipid metabolism had also been explored in a number of studies based on cell lines and mouse models. These results demonstrated that HBV replication or expression induced extensive and diverse changes in hepatic lipid metabolism, by not only activating expression of some critical lipogenesis and cholesterolgenesis-related proteins but also upregulating fatty acid oxidation and bile acid synthesis. Moreover, increasing studies found some potential targets to inhibit HBV replication or expression by decreasing or enhancing certain lipid metabolism-related proteins or metabolites. Therefore, in this article, we comprehensively reviewed these publications and revealed the connections between clinical observations and experimental findings to better understand the interaction between hepatic lipid metabolism and HBV infection. However, the available data are far from conclusive, and there is still a long way to go before clarifying the complex interaction between HBV infection and hepatic lipid metabolism.

Cerebral Insulin Bolus Revokes the Changes in Hepatic Lipid Metabolism Induced by Chronic Central Leptin Infusion.

Central actions of leptin and insulin on hepatic lipid metabolism can be opposing and the mechanism underlying this phenomenon remains unclear. Both hormones can modulate the central somatostatinergic system that has an inhibitory effect on growth hormone (GH) expression, which plays an important role in hepatic metabolism. Using a model of chronic central leptin infusion, we evaluated whether an increase in central leptin bioavailability modifies the serum lipid pattern through changes in hepatic lipid metabolism in male rats in response to an increase in central insulin and the possible involvement of the GH axis in these effects. We found a rise in serum GH in leptin plus insulin-treated rats, due to an increase in pituitary GH mRNA levels associated with lower hypothalamic somatostatin and pituitary somatostatin receptor-2 mRNA levels. An augment in hepatic lipolysis and a reduction in serum levels of non-esterified fatty acids (NEFA) and triglycerides were found in leptin-treated rats. These rats experienced a rise in lipogenic-related factors and normalization of serum levels of NEFA and triglycerides after insulin treatment. These results suggest that an increase in insulin in leptin-treated rats can act on the hepatic lipid metabolism through activation of the GH axis.

Perilipin 5 S155 phosphorylation by PKA is required for the control of hepatic lipid metabolism and glycemic control

Perilipin 5 (PLIN5) is a lipid-droplet-associated protein that coordinates intracellular lipolysis in highly oxidative tissues and is thought to regulate lipid metabolism in response to phosphorylation by protein kinase A (PKA). We sought to identify PKA phosphorylation sites in PLIN5 and assess their functional relevance in cultured cells and the livers of mice. We detected phosphorylation on S155 and identified S155 as a functionally important site for lipid metabolism. Expression of phosphorylation-defective PLIN5 S155A in Plin5 null cells resulted in decreased rates of lipolysis and triglyceride-derived fatty acid oxidation. FLIM-FRET analysis of protein-protein interactions showed that PLIN5 S155 phosphorylation regulates PLIN5 interaction with adipose triglyceride lipase at the lipid droplet, but not with α-β hydrolase domain-containing 5. Re-expression of PLIN5 S155A in the liver of Plin5 liver-specific null mice reduced lipolysis compared with wild-type PLIN5 re-expression, but was not associated with other changes in hepatic lipid metabolism. Furthermore, glycemic control was impaired in mice with expression of PLIN5 S155A compared with mice expressing PLIN5. Together, these studies demonstrate that PLIN5 S155 is required for PKA-mediated lipolysis and builds on the body of evidence demonstrating a critical role for PLIN5 in coordinating lipid and glucose metabolism.

Hepatic lipid metabolism in adult rats using early weaning models: sex-related differences.

Non-pharmacological early weaning (NPEW) induces liver damage in male progeny at adulthood; however, pharmacological early weaning (PEW) does not cause this dysfunction. To elucidate this difference in liver dysfunction between these two models and determine the phenotype of female offspring, de novo lipogenesis, β-oxidation, very low-density lipoprotein (VLDL) export, and gluconeogenesis in both sexes were investigated in the adult Wistar rats that were weaned after a normal period of lactation (control group) or early weaned either by restriction of access to the dams' teats (NPEW group) or by reduction of dams' milk production with bromocriptine (PEW group). The offspring received standard diet from weaning to euthanasia (PN180). NPEW males had higher plasma triglycerides and TyG index, liver triglycerides, and cholesterol by de novo lipogenesis, which leads to intracellular lipids accumulation. As expected, hepatic morphology was preserved in PEW males, but they showed increased liver triglycerides. The only molecular difference between PEW and NPEW males was in acetyl-CoA carboxylase-1 (ACC-1) and stearoyl-CoA desaturase-1 (SCD-1), which were lower in PEW animals. Both early weaning (EW) females had no changes in liver cholesterol and triglyceride contents, and the hepatic cytoarchitecture was preserved. The expression of microsomal triglyceride transfer protein was increased in both the female EW groups, which could constitute a protective factor. The changes in hepatic lipid metabolism in EW offspring were less marked in females. EW impacted in the hepatic cytoarchitecture only in NPEW males, which showed higher ACC-1 and SCD-1 when compared to the PEW group. As these enzymes are lipogenic, it could explain a worsened liver function in NPEW males.

Excessive early-life cholesterol exposure may have later-life consequences for nonalcoholic fatty liver disease.

The in utero and immediate postnatal environments are recognized as critical windows of developmental plasticity where offspring are highly susceptible to changes in the maternal metabolic milieu. Maternal hypercholesterolemia (MHC) is a pathological condition characterized by an exaggerated rise in maternal serum cholesterol during pregnancy which can program metabolic dysfunction in offspring, including dysregulation of hepatic lipid metabolism. Although there is currently no established reference range MHC, a loosely defined cutoff point for total cholesterol >280 mg/dL in the third trimester has been suggested. There are several unanswered questions regarding this condition particularly with regard to how the timing of cholesterol exposure influences hepatic lipid dysfunction and the mechanisms through which these adaptations manifest in adulthood. Gestational hypercholesterolemia increased fetal hepatic lipid concentrations and altered lipid regulatory mRNA and protein content. These early changes in hepatic lipid metabolism are evident in the postweaning environment and persist into adulthood. Further, changes to hepatic epigenetic signatures including microRNA (miR) and DNA methylation are observed in utero, at weaning, and are evident in adult offspring. In conclusion, early exposure to cholesterol during critical developmental periods can predispose offspring to the early development of nonalcoholic fatty liver disease (NAFLD) which is characterized by altered regulatory function beginning in utero and persisting throughout the life cycle.

Developmental changes in hepatic lipid metabolism of chicks during the embryonic periods and the first week of posthatch

The liver is the main site of de novo lipogenesis in poultry, and hepatic lipid metabolism disorder will lead to excessive abdominal fat deposition or fatty liver disease, finally causing huge economic loss. The present study was conducted to investigate developmental changes in hepatic lipid metabolism of chicks from embryonic periods to the first week after hatching. Liver samples were collected from embryonic day 11 (E11) to the age of day 7 posthatch (D7) for lipid metabolism analysis. Hematoxylin–eosin and Oil Red O staining analysis showed that hepatic lipids increased gradually during embryonic period and declined posthatch; The sum of hepatic triglycerides and cholesterol reached the peak at E19 and D1 by ELISA analysis (P < 0.05). Acetyl-CoA carboxylase, fatty acid synthase, and acyl-CoA desaturase 1 mRNA expression in the liver were higher from E17 to D1 with the peak at E19 when compared with those at E13 and E15 (P < 0.05). Hepatic elongase of very long-chain fatty acids 6 and microsomal triglyceride transfer protein mRNA abundance were lower during embryonic periods but reached relative higher level after hatching (P < 0.05). On the contrary, hepatic carbohydrate response element binding protein (ChREBP), carnitine palmitoyltransferase 1, and peroxisome proliferators–activated receptor α expression were higher during embryonic periods but decreased posthatch (P < 0.05). The mRNA abundance of sterol-regulatory element binding protein 1c was the lowest at E13 and E15, then increased gradually from E17 to D1, while decreased from D3 to D7 little by little (P < 0.05). In summary, hepatic lipogenesis genes have different expression patterns during the embryonic periods and the first week of posthatch, which might be activated by ChREBP during embryonic periods; fatty acid oxidation was enhanced around the hatched day but declined posthatch. These findings will broaden the understanding of physiological characteristics and dynamic pattern about hepatic lipid metabolism in chicks.

Lipophagy mediated carbohydrate-induced changes of lipid metabolism via oxidative stress, endoplasmic reticulum (ER) stress and ChREBP/PPARγ pathways.

High-carbohydrate diets (HCD) can induce the occurrence of nonalcoholic fatty liver disease (NAFLD), characterized by dramatic accumulation of hepatic lipid droplets (LDs). However, the potential molecular mechanisms are still largely unknown. In this study, we investigated the role of autophagy in the process of HCD-induced changes of hepatic lipid metabolism, and to examine the process of underlying mechanisms during these molecular contexts. We found that HCD significantly increased hepatic lipid accumulation and activated autophagy. Using primary hepatocytes, we found that HG increased lipid accumulation and stimulated the release of NEFA by autophagy-mediated lipophagy, and that lipophagy significantly alleviated high glucose (HG)-induced lipid accumulation. Oxidative and endoplasmic reticulum (ER) stress pathways played crucial regulatory roles in HG-induced lipophagy activation and HG-induced changes of lipid metabolism. Further investigation found that HG-activated lipophagy and HG-induced changes of lipid metabolism were via enhancing carbohydrate response element-binding protein (ChREBP) DNA binding capacity at PPARγ promoter region, which in turn induced transcriptional activation of the key genes related to lipogenesis and autophagy. The present study, for the first time, revealed the novel mechanism for lipophagy mediating HCD-induced changes of lipid metabolism by oxidative stress and ER stress, and ChREBP/PPARγ pathways. Our study provided innovative evidence for the direct relationship between carbohydrate and lipid metabolism via ChREBP/PPARγ pathway.

Angiotensinogen in Hepatocytes Contributes to Western Diet-Induced Liver Steatosis

Background: Non-alcoholic fatty liver disease (NAFLD) is considered as the liver manifestation of metabolic disorders. Previous studies hinted that renin-angiotensin system (RAS) played a multi-faceted role in NAFLD. Angiotensinogen (AGT) is the first precursor of RAS, whose deficiency profoundly impacts RAS bioactivity and regulates metabolic disorders. Here we investigated the role AGT acted in hepatosteatosis. Methods: Mice with AGT floxed alleles or hepatocyte-specific AGT deficiency (hepAGT-/-) in C57BL/6 background were fed with western diet or normal laboratory diet. Mouse body weight and diet consumption were weighed weekly. Glucose and insulin tolerance tests were carried out to access insulin resistance. Adipose tissues, liver, and plasma were collected at termination. Experiments including triglyceride measurement, histological analysis, quantitative PCR, western blot of liver tissues were performed to study changes in hepatic lipid metabolism. Findings: Hepatocyte-specific AGT knockout mice resisted to western diet-induced body weight gain, liver steatosis with preserved insulin sensitivity. Liver expressions of proteins related to de novo lipogenesis and lipid storage were remarkably decreased in hepAGT-/- mice. Interpretation: Hepatocyte-specific AGT contributes to fat-enriched diet-induced liver steatosis via regulating liver de novo lipogenesis mediated by Srebp1c pathway and lipid storage related proteins. Funding: This work was supported by grants from Grant from National Natural Science Foundation of China (No. 81870292 for J.W., No. 81500876 for Y.X.), Grants from National Key Research and Development Program of China (No.2016YFC1301204 for J.W.), and Grants from Natural Science Foundation of Zhejiang Province (No. LQ16H020003 for Y.X.). Declaration of Interest: None. Ethical Approval: All animal studies were approved by the Animal Care and Use Committee of Zhejiang University in accordance with the Chinese guidelines for the care and use of laboratory animals.

Upstream regulators of apoptosis mediates methionine-induced changes of lipid metabolism

Although the role of methionine (Met), as precursor for l-carnitine synthesis, in the regulation of lipid metabolism has been explored. Met seems to have tissue- and species-specific regulatory effect on lipid metabolism, implying that the mechanisms in Met regulation of lipid metabolism is complex and may involve the upstream regulatory pathway of lipid metabolism. The present study was performed to determine the mechanism of apoptosis signaling pathways mediating Met-induced changes of hepatic lipid deposition and metabolism in fish, and compare the differences of the mechanisms between the fish and mammals. By iTRAQ-based quantitative proteome analyses, we found that both dietary Met deficiency and excess evoked apoptosis signaling pathways, increased hepatic lipid deposition and caused aberrant hepatic lipid metabolism of yellow catfish Pelteobagrus fulvidraco. Using primary hepatocytes from P. fulvidraco, inhibition of caspase by Z-VAD-FMK blocked the apoptotic signaling pathways with a concomitant reversal of Met deficiency- and excess-induced increase of lipid deposition, indicating that apoptosis involved the Met-mediated changes of hepatic lipid metabolism. Moreover, we explored the roles of three upstream apoptotic signaling pathways (PI3K/AKT-TOR pathway, cAMP/PKA/CREB pathway and LKB1/AMPK-FOXO pathway) influencing hepatic lipid metabolism of P. fulvidraco. The three upstream pathways participated in apoptosis mediating Met-induced changes of lipid metabolism in P. fulvidraco. At last, HepG2 cell line was used to compare the similarities of mechanisms in apoptosis mediating Met-induced changes of lipid metabolism between fish and mammals. Although several slight differences existed, apoptosis mediated the Met-induced changes of lipid metabolism between fish and mammals. The present study reveals novel apoptosis-relevant signal transduction axis which mediates the Met-induced changes of lipid metabolism, which will help understand the mechanistic link between apoptosis and lipid metabolism, and highlight the importance of the evolutionary conservative apoptosis signaling axis in regulating Met–induced changes of hepatic lipid metabolism.

Adaptations of hepatic lipid metabolism and mitochondria in dairy cows with mild fatty liver

The inevitable deficiency in nutrients and energy at the onset of lactation requires an optimal adaptation of the hepatic metabolism to overcome metabolic stress. Fatty liver is one of the main health disorders after parturition. Therefore, to investigate changes in hepatic lipid metabolic status and mitochondria in dairy cows with mild fatty liver, liver and blood samples were collected from healthy cows (n = 15) and cows with mild fatty liver (n = 15). To determine the effects of palmitic acids (PA), one of the major component of fatty acids, on lipid metabolism and mitochondria in vitro, calf hepatocytes were isolated from healthy calves and treated with various concentrations of PA (0, 50, 100, and 200 μM). Dairy cows with mild fatty liver displayed hepatic lipid accumulation. The protein levels of sterol regulatory element-binding protein 1c (SREBP-1c) and peroxisome proliferator-activated receptor-α (PPARα) and mRNA levels of acetyl CoA carboxylase 1 (ACC1), fatty acid synthase (FAS), acyl-CoA oxidase (ACO), and carnitine palmitoyltransferase 1A (CPT1A) were significantly higher in dairy cows with mild fatty liver than in control cows. The hepatic mitochondrial DNA content, mRNA levels of oxidative phosphorylation complexes I to V (CO 1-V), protein levels of cytochrome c oxidase subunit IV (COX IV), voltage dependent anion channel 1 (VDAC1), peroxisome proliferator activated receptor-γ coactivator-1α (PGC-1α) and nuclear respiratory factor 1 (NRF1), and adenosine triphosphate (ATP) content were all markedly increased in the liver of dairy cows with mild fatty liver compared with healthy cows. The PA treatment significantly increased lipid accumulation; protein levels of SREBP-1c and PPARα; and mRNA levels of ACC1, FAS, ACO, and CPT1A in calf hepatocytes. Moreover, the mitochondrial DNA content, mRNA levels of CO 1-V, protein levels of COX IV, VDAC1, PGC-1α, NRF1, mitochondrial transcription factor A, and ATP content were significantly increased in PA-treated hepatocytes compared with control hepatocytes. The protein level of mitofusin-2 was significantly decreased in PA-treated groups. In conclusion, lipid synthesis and oxidation, number of mitochondria, and ATP production were increased in the liver of dairy cows with mild fatty liver and PA-treated calf hepatocytes. These changes in hepatic mitochondria and lipid metabolism may be the adaptive mechanism of dairy cows with mild fatty liver.

CREB element is essential for unfolded protein response (UPR) mediating the Cu-induced changes of hepatic lipogenic metabolism in Chinese yellow catfish (Pelteobagrus fulvidraco)

The present study was conducted to explore the underlying mechanism of unfolded protein response (UPR) mediating the Cu-induced changes of hepatic lipogenic metabolism in a low vertebrate, freshwater teleost yellow catfish Pelteobagrus fulvidraco. To this end, three experiments were conducted. In Exp. 1, we cloned the regions of grp78, perk, ire-1α and atf-6α promoters, and found that multiple cAMP-response element binding protein (CREB) binding sites were identified in their promoter regions. Furthermore, these CREB binding sites played crucial role in transcriptional regulation of UPR. In Exp. 2, the involvement of perk, ire-1α and atf-6α in Cu-induced changes of hepatic lipid metabolism was confirmed by specific miRNA. In Exp. 3, the regulatory mechanism of CREB underlying UPR mediating Cu-induced hepatic lipogenic metabolism were investigated. Cu induced UPR via the activation of CREB binding sites in the promoter regions of grp78, perk, ire-1α and atf-6α. In addition, the inhibition of CREB markedly attenuated the Cu-induced up-regulation of hepatic lipogenic metabolism in hepatocytes. This conclusion was further supported by the results from the trial of CREB over-expression. Taken together, the present study indicated that CREB was essential for UPR mediating Cu-induced lipogenic metabolism, supporting a mechanistic link among CREB, UPR and Cu-induced changes of lipid metabolism.