Oridonin restores hepatic lipid homeostasis in an LXRa-ATGL/EPT1 axis-dependent manner

Hepatosteatosis is characterized by abnormal accumulation of triglycerides(TG),leading to prolonged and chronic inflammatory infiltration.To date,there is still a lack of effective and economical therapies for hepatosteatosis.Oridonin(ORI)is a major bioactive component extracted from the traditional Chinese medicinal herb Rabdosia rubescens.In this paper,we showed that ORI exerted significant protective effects against hepatic steatosis,inflammation and fibrosis,which was dependent on LXRa signaling.It is reported that LXRa regulated lipid homeostasis between triglyceride(TG)and phosphatidylethanolamine(PE)by promoting ATGL and EPT1 expression.Therefore,we implemented the lipidomic strategy and luciferase reporter assay to verify that ORI contributed to the homeostasis of lipids via the regulation of the ATGL gene associated with TG hydrolysis and the EPT1 gene related to PE synthesis in a LXRadependent manner,and the results showed the TG reduction and PE elevation.In detail,hepatic TG overload and lipotoxicity were reversed after ORI treatment by modulating the ATGL and EPT1 genes,respectively.Taken together,the data provide mechanistic insights to explain the bioactivity of ORI in attenuating TG accumulation and cytotoxicity and introduce exciting opportunities for developing novel natural activators of the LXRa-ATGL/EPT1 axis for pharmacologically treating hepatosteatosis and metabolic disorders.

Liver-specific Reduction of Mfn2 Protein by RNAi Results in Impaired Glycometabolism and Lipid Homeostasis in BALB/c Mice

Mitofusin-2 （Mfn2） gene expression is positively correlated with insulin sensitivity in patients with type 2 diabetes. However, it is unclear if Mfn2 is involved in carbohydrate metabolism and lipid homeostasis. In order to investigate the specific functions of Mfn2 in glycometabolism and lipid homeostasis in BALB/c mice, a RNA interference technique-mediated hydrodynamic injection was developed, in which short hairpin RNAs （shRNAs） were used to inhibit the Mfn2 expression in vivo. Seventy-two mice were randomly divided into two groups： the Mfn2 reduction group （Mfn2/shRNA） and the negative control group （NC）. Intraperitoneal glucose tolerance tests and intraperitoneal insulin tolerance tests were used to evaluate glycometabolism and insulin sensitivity. D-（3-3H） glucose or 3H2O was injected into the tail vein or intraperitoneally to facilitate the calculation of the rate of hepatic glucose production and fatty acid synthesis in vivo. The results showed that, in Mfn2/shRNA mice, the liver Mfn2 protein was significantly decreased, and fasting blood glucose concentrations were increased by approximately 48%, when compared with the NC mice. In parallel with the changes in fasting glucose levels, hepatic glucose production was significantly elevated in Mfn2/shRNA mice. When insulin was administrated, these mice exhibited impaired insulin tolerance. It was also found that the reduction of Mfn2 markedly decreased the rate of fatty acid synthesis in the liver, and the Mfn2/shRNA mice exhibited hypertriglyceridema. Taken together, our results indicate that Mfn2 plays an important role in maintaining glucose and lipid homeostasis, and in the development of insulin resistance in vivo.

Disruption of hepatic lipid homeostasis is involved in valproate-induced hepatotoxicity

OBJECTIVE To investigate the mechanism underlying valproate(VPA)-induced hepatic hepatotoxicity.METHODS C57B/6J mice were given VPA at500 mg·kg-1·d-1by intragastric administration for 14 consecutive days,while the control group received the same volume of physiologic saline by intragastric administration for same days.Mice were sacrificed 24 h after the last administration.Blood samples were collected for plasma biochemical assays.Liver was fixed in 10%neutral buffered formalin for histopathological analysis,and RNA extraction.mR NA for selected genes expression encoding proteins key to fatty acid synthesis,triglyceride synthesis,fatty acid oxidation,phosphatidylcholine synthesis,and lipid uptake were measured using quantitative real-time PCR.RESULTS We found that VPA treatment induced hepatic injury in mice as evidenced by increased ALP,ATP,ASP,GGT,and LDH.Histopathological analysis of the liver in mice treated with VPA showed increased microvesicular steatosis in cytoplasm.More importantly,VPA treatment increased the m RNA expressions of sterol regulatory element binding protein(SREBP)-1c,peroxisome proliferator-activated receptor(PPAR)γ,diacylgycerol acyltransferase(DGAT)2,and cluster of differentiation(CD)36,while the mR NA levels of stearoyl-Co A desaturase(SCD)1,DGAT1,liver X receptorsα(LXRα),carnitine palmitoyltransferase(CPT)1,malonyl coenzyme A decarboxylase(MCD),uncoupling protein(UCP)2,phosphatidylethanolamine N-methyltransferase(PEMT),and pregnenolone X receptor(PXR)displayed significant decrease.CONCLUSION Our data showed that VPA induced disruption of hepatic lipid homeostasis,which could be helpful for a better under-standing of the mechanism underlying VPA-induced hepatotoxicity and for a better use of VPA.

Long-chain acyl-CoA synthetase regulates systemic lipid homeostasis via glycosylation-dependent lipoprotein production

Interorgan lipid transport is crucial for organism development and the maintenance of physiological function.Here,we demonstrate that Drosophila long-chain acyl-CoA synthetase(dAcsl),which catalyzes the conversion of fatty acids into acyl-coenzyme As(acyl-CoAs),plays a critical role in regulating systemic lipid homeostasis.dAcsl deficiency in the fat body led to the ectopic accumulation of neutral lipids in the gut,along with significantly reduced lipoprotein contents in both the fat body and hemolymph.The aberrant phenotypes were rescued by fat body-specific overexpression of apolipophorin.A multi-omics investigation comprising lipidomics,metabolomics,and proteomics in conjunction with genetic screening revealed that glycosylation processes were suppressed in dAcsl knockdown flies.Overexpression of CG9035,human ortholog of which is implicated in the congenital disorder of glycosylation,ame-liorated gut lipid accumulation in Drosophila.Aberrant lipoprotein glycosylation led to accelerated proteasome-related degradation and induced ER stress in dAcsl knockdown flies,impairing lipoprotein release into the circulation which compromised interorgan lipid transport between the fat body and the gut.Inhibition of ubiquitin-proteasome-dependent degradation alleviated the phenotype of gut ectopic fat accumulation in dAcsl knockdown flies.Finally,we verified that ACSL4,the human homolog of dAcsl,also regulated lipoprotein levels in HepG2 cells,indicating that the role of dAcsl in modulating lipoprotein secretion and systemic lipid homeostasis is possibly conserved in humans.

Nuclear transcription factors and lipid homeostasis in liver

The liver plays a major role in the regulation , glucose, lipid and energy metabolism. Increasd hepatic fat deposit is a very common feature in obese, insulin-resistant patients, in metabolic syndrome, alcoholic steatohepatitis （ASH） and nonalchoholic fatty liver disaseas （NAFLD）. As a central organ for whole body lipid metabolism, disruption of the normal mechanisms for synthesis, transport and removal/ metabolism of long-chain fatty acids and triglycerides are the basis for the development of fatty liver. The exact mechanisms that link hepatic lipid accumulation, impaired glucose metabolism, and insulin resistance are unknown, but increasing evidence suggest that nuclear transcription factors play important roles. Members of the nuclear receptor superfamily, especially the peroxisome proliferator-activated receptors （PPARs） and the liver X receptor （LXR）, other factors such as sterol regulatory element binding proteins （SREBPs）, carbohydrate- response element-binding protein （ChREBP）, and nuclear transcription fator-κB （NF-κB） have emerged as dominant regulators of these processes, but the relative role of each of these factors in fatty liver disease is still undefined.

The molecular pathogenic role of inflammatory stress in dysregulation of lipid homeostasis and hepatic steatosis

Non-alcoholic Fatty Liver Disease(NAFLD)is becoming the leading cause of chronic liver injury in developed countries and China.Chronic systemic inflammation plays a decisive role and is fundamental in the progression of NAFLD from simple steatosis(SS)toward higher risk nonalcoholic steatohepatitis(NASH)states.However,the exact mechanisms by which inflammation leading to NASH are incompletely understood.In this review,we focus the role of the cross talk between inflammation and lipid homeostasis on the progression of NAFLD.

The LXRB-SREBP1 network regulates lipogenic homeostasis by controlling the synthesis of polyunsaturated fatty acids in goat mammary epithelial cells

Background:In rodents,research has revealed a role of liver X receptors(LXR) in controlling lipid homeostasis and regulating the synthesis of polyunsaturated fatty acids(PUFA).Recent data suggest that LXRB is the predominant LXR subtype in ruminant mammary cells,but its role in lipid metabolism is unknown.It was hypothesized that LXRB plays a role in lipid homeostasis via altering the synthesis of PUFA in the ruminant mammary gland.We used overexpression and knockdown of LXRB in goat primary mammary epithelial cells(GMEC) to evaluate abundance of lipogenic enzymes,fatty acid profiles,content of lipid stores and activity of the stearoyl-Co A desaturase(SCD1) promoter.Results:Overexpression of LXRB markedly upregulated the protein abundance of LXRB while incubation with si RNA targeting LXRB markedly decreased abundance of LXRB protein.Overexpression of LXRB plus T0901317(T09,a ligand for LXR) dramatically upregulated SCD1 and elongation of very long chain fatty acid-like fatty acid elongases 5–7(ELOVL 5–7),which are related to PUFA synthesis.Compared with the control,cells overexpressing LXRB and stimulated with T09 had greater concentrations of C16:0,16:1,18:1n7,18:1n9 and C18:2 as well as desaturation and elongation indices of C16:0.Furthermore,LXRB-overexpressing cells incubated with T09 had greater levels of triacylglycerol and cholesterol.Knockdown of LXRB in cells incubated with T09 led to downregulation of genes encoding elongases and desaturases.Knockdown of LXRB attenuated the increase in triacylglycerol and cholesterol that was induced by T09.In cells treated with dimethylsulfoxide,knockdown of LXRB increased the concentration of C16:0 at the expense of C18:0,while a significant decrease in C18:2 was observed in cells incubated with both si LXRB and T09.The abundance of sterol regulatory element binding transcription factor 1 precursor(p SREBP1) and its mature fragment(n SREBP1) was upregulated by T09,but not LXRB overexpression.In the cells cultured with T09,knockdown of LXRB downregulated the abundance for p SREBP1 and n SREBP1.Luciferase reporter assays revealed that the activities of wild type SCD1 promoter or fragment with SREBP1 response element(SRE) mutation were decreased markedly when LXRB was knocked down.Activity of the SCD1 promoter that was induced by T09 was blocked when the SRE mutation was introduced.Conclusion:The current study provides evidence of a physiological link between the LXRB and SREBP1 in the ruminant mammary cell.An important role was revealed for the LXRB-SREBP1 network in the synthesis of PUFA via the regulation of genes encoding elongases and desaturases.Thus,targeting this network might elicit broad effects on lipid homeostasis in ruminant mammary gland.

Polyphenols and pectin enriched golden kiwifruit (Actinidia chinensis) alleviates high fructose-induced glucolipid disorders and hepatic oxidative damage in rats:in association with improvement of fatty acids metabolism

This study aimed to investigate the protective effects of fleshes from two Actinidia chinensis(ACF), pericarps from two A. chinensis(ACP), and fleshes with pericarps from two A. chinensis(ACFP)on high fructose(HF)-instigated dyslipidemia, hepatic steatosis, oxidative stress, insulin resistance, and fatty acid metabolism disorders in rats. In general, the above abnormalities were improved after 10 weeks intervention of ACF, ACP, and ACFP. Especially, ACFP considerably ameliorated HF-induced abnormal changes in body weight gain, serum TC, TG, LDL-C and HDL-C levels, as well as serum and hepatic SFAs, MUFAs and PUFAs contents. ACFP also alleviated HF-induced hyperglycemia and hyperinsulinemia, stabilized HF-caused increase in hepatic MDA and serum ALT, AST levels, and restored HF-declined hepatic T-SOD and GSH-Px activities. Besides, histopathology of the liver further endorsed the protective effects of ACFP on hepatocellular injury. Moreover, ACFP increased HF-dropped acetic, propionic and butyric acid levels. Overall, ACFP employs more efficacious protective effects against HF-induced metabolic disorders and liver damage than ACF and ACP. This study delivers a scientific foundation for developing kiwifruit(counting peel)-based dietary supplements for those with glucolipid-metabolic disorders and liver damage.

Thrombin increases the expression of cholesterol 25-hydroxylase in rat astrocytes after spinal cord injury

Astrocytes are important cellular centers of cholesterol synthesis and metabolism that help maintain normal physiological function at the organism level.Spinal cord injury results in aberrant cholesterol metabolism by astrocytes and excessive production of oxysterols,which have profound effects on neuropathology.25-Hydroxycholesterol(25-HC),the main product of the membrane-associated enzyme cholesterol-25-hydroxylase(CH25H),plays important roles in mediating neuroinflammation.However,whether the abnormal astrocyte cholesterol metabolism induced by spinal cord injury contributes to the production of 25-HC,as well as the resulting pathological effects,remain unclear.In the present study,spinal cord injury-induced activation of thrombin was found to increase astrocyte CH25H expression.A protease-activated receptor 1 inhibitor was able to attenuate this effect in vitro and in vivo.In cultured primary astrocytes,thrombin interacted with protease-activated receptor 1,mainly through activation of the mitogen-activated protein kinase/nuclear factor-kappa B signaling pathway.Conditioned culture medium from astrocytes in which ch25h expression had been knocked down by siRNA reduced macrophage migration.Finally,injection of the protease activated receptor 1 inhibitor SCH79797 into rat neural sheaths following spinal cord injury reduced migration of microglia/macrophages to the injured site and largely restored motor function.Our results demonstrate a novel regulatory mechanism for thrombin-regulated cholesterol metabolism in astrocytes that could be used to develop anti-inflammatory drugs to treat patients with spinal cord injury.

Depletion of stearoyl-CoA desaturase(scd) leads to fatty liver disease and defective mating behavior in zebrafish

Stearyl coenzyme A desaturase(SCD), also known as delta-9 desaturase, catalyzes the rate-limiting step in the formation of monounsaturated fatty acids.In mammals, depletion or inhibition of SCD activity generally leads to a decrease in triglycerides and cholesteryl esters. However, the endogenous role of scd in teleost fish remains unknown. Here, we generated a zebrafish scd mutant(scd-/-) to elucidate the role of scd in lipid metabolism and sexual development. Gas chromatography-mass spectrometry(GC-MS) showed that the scd-/- mutants had increased levels of saturated fatty acids C16:0 and C18:0, and decreased levels of monounsaturated fatty acids C16:1 and C18:1. The mutant fish displayed a short stature and an enlarged abdomen during development. Unlike Scd-/ -mammals, the scd-/- zebrafish showed significantly increased fat accumulation in the whole body,especially in the liver, leading to hepatic mitochondrial dysfunction and severe cell apoptosis.Mechanistically, srebf1, a gene encoding a transcriptional activator related to adipogenesis,acc1 and acaca, genes involved in fatty acid synthesis, and dgat2, a key gene involved in triglyceride synthesis, were significantly upregulated in mutant livers to activate fatty acid biosynthesis and adipogenesis. The scd-/- males exhibited defective natural mating behavior due to defective genital papillae but possessed functional mature sperm. All defects in the scd-/- mutants could be rescued by ubiquitous transgenic overexpression of scd. In conclusion, our study demonstrates that scd is indispensable for maintaining lipid homeostasis and development of secondary sexual characteristics in zebrafish.

硅对盐胁迫下枣组培苗生根培养效果、体内离子稳态及膜脂过氧化的影响

以泗洪大枣微茎段增殖扩繁苗为试材,研究了NaCl 75 mmol/L胁迫下生根培养基中加Si(K2SiO30.75 mmol/L)与否对枣树组培苗生根培养效果、体内离子稳态及膜脂过氧化的影响。结果表明:盐胁迫下枣树微茎段外植体成活率和生根率显著降低,生根枣苗的侧根条数、侧根平均长度、株高和单株重量均显著减小,盐胁迫下加Si处理的这些指标则显著升高或增大而与对照无显著性差异。盐胁迫下枣树组培苗体内Na+、Cl-含量均较对照显著升高,K+/Na+显著减小;盐胁迫下加Si枣苗体内Cl-含量减少,与对照无显著差异;Na+含量和K+/Na+虽然显著高于对照,但显著低于不加Si处理。盐胁迫下生根培养基中加Si与不加Si相比,枣树组培苗体内谷胱甘肽过氧化物酶(GPX)等抗氧化酶系统应激响应明显趋于平缓,细胞质膜透性显著减小,丙二醛(MDA)含量则无显著差异。说明,盐胁迫下加Si优化枣树生根培养基条件,增强组培枣苗对盐分离子的选择性吸收功能,利于保持盐胁迫下枣树组培苗体内的离子稳态,诱导对膜脂过氧化作用抗性的提高。

Carboxylesterase 1 family knockout alters drug disposition and lipid metabolism

The mammalian carboxylesterase 1(Ces1/CES1)family comprises several enzymes that hydrolyze many xenobiotic chemicals and endogenous lipids.To investigate the pharmacological and physiological roles of Ces1/CES1,we generated Ces1 cluster knockout(Ces1^(-/-))mice,and a hepatic human CES1 transgenic model in the Ces1^(-/-)background(TgCES1).Ces1^(-/-)mice displayed profoundly decreased conversion of the anticancer prodrug irinotecan to SN-38 in plasma and tissues.TgCES1 mice exhibited enhanced metabolism of irinotecan to SN-38 in liver and kidney.Ces1 and hCES1 activity increased irinotecan toxicity,likely by enhancing the formation of pharmacodynamically active SN-38.Ces1^(-/-)mice also showed markedly increased capecitabine plasma exposure,which was moderately decreased in TgCES1 mice.Ces1^(-/-)mice were overweight with increased adipose tissue,white adipose tissue inflammation(in males),a higher lipid load in brown adipose tissue,and impaired blood glucose tolerance(in males).These phenotypes were mostly reversed in TgCES1 mice.TgCES1 mice displayed increased triglyceride secretion from liver to plasma,together with higher triglyceride levels in the male liver.These results indicate that the carboxylesterase 1 family plays essential roles in drug and lipid metabolism and detoxification.Ces1^(-/-)and TgCES1 mice will provide excellent tools for further study of the in vivo functions of Ces1/CES1 enzymes.

PITPNC1 promotes the thermogenesis of brown adipose tissue under acute cold exposure

Brown adipose tissue (BAT) plays an essential role in non-shivering thermogenesis. The phosphatidylinositol transfer protein, cytoplasmic 1 (PITPNC1) is identified as a lipid transporter that reciprocally transfers phospholipids between intracellular membrane structures. However, the physiological significance of PITPNC1 and its regulatory mechanism remain unclear. Here, we demonstrate that PITPNC1 is a key player in thermogenesis of BAT. While Pitpnc1^(−/−) mice do not differ with wildtype mice in body weight and insulin sensitivity on either chow or high-fat diet, they develop hypothermia when subjected to acute cold exposure at 4℃. The Pitpnc1^(−/−) brown adipocytes exhibit defective β-oxidation and abnormal thermogenesis-related metabolism pathways in mitochondria. The deficiency of lipid mobilization in Pitpnc1^(−/−) brown adipocytes might be the result of excessive accumulation of phosphatidylcholine and a reduction of phosphatidic acid. Our findings have uncovered significant roles of PITPNC1 in mitochondrial phospholipid homeostasis and BAT thermogenesis.