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.

Mechanistic action of the acute toxicity of Bajitian(Morinda officinalis)in zebrafish embryos

Objectives:To investigate acute toxicity of Bajitian(Morinda officinalis)in zebrafish embryos.Methods:Zebrafish embryos at 48-h post fertilization(hpf)were exposed to Bajitian ethanol extract for72 h.The causative action of a delay in yolk sac absorption by Bajitian was investigated by RT-PCR analysis of lipid metabolism-related microsomal triglyceride transfer protein(MTP),apolipoprotein CII(ApoC2)and lipogenesis-related liver x receptor(LXR)genes.The effect of Bajitian eliciting an inflammatory response was studied by exposing 72 hpf myeloperoxidase(MPO):GFP transgenic zebrafish embryos to Bajitian extract for 4 h.Assessment was done by TUNEL,caspase-3/7,and RT-PCR analysis of the apoptosis related pathway B-cell lymphoma 2 associated X protein(Bax),Nuclear factor kappa-lightchain-enhancer of activated B cells(NF-k B)genes,neutrophil development-related stem cell leukaemia(SCL)and transcription factor PU.1 genes,to reveal the causative action of Bajitian reducing neutrophils.Results:RT-PCR analysis found that Bajitian extract had no effect on the expression of MTP or ApoC2 genes,but upregulated LXR gene,which might explain the delay in yolk sac absorption.Analysis of the inflammatory response showed that compared with negative controls,Bajitian extract significantly(P<.05)reduced the number of neutrophils in MPO:GFP embryos.TUNEL,caspase-3/7,and RT-PCR analysis of Bax and NF-k B genes found that Bajitian extract did not trigger the cell apoptosis.Further RT-PCR analysis found that Bajitian extract did not affect SCL expression,but did lead to down-regulation of PU.1.The inhibition of neutrophil development/differentiation may explain the decline in the total number of neutrophils following Bajitian treatment,which could be attributed to the anti-inflammatory effects found clinically for this drug.Conclusions:This study demonstrated that Bajitian caused a delay in yolk sac absorption and a decrease neutrophil in zebrafish embryos,which may be related to the inhibition of neutrophil development.

Liver as a new target organ in Alzheimer's disease:insight from cholesterol metabolism and its role in amyloid-beta clearance

Alzheimer's disease,the primary cause of dementia,is characterized by neuropathologies,such as amyloid plaques,synaptic and neuronal degeneration,and neurofibrillary tangles.Although amyloid plaques are the primary characteristic of Alzheimer's disease in the central nervous system and peripheral organs,targeting amyloid-beta clearance in the central nervous system has shown limited clinical efficacy in Alzheimer's disease treatment.Metabolic abnormalities are commonly observed in patients with Alzheimer's disease.The liver is the primary peripheral organ involved in amyloid-beta metabolism,playing a crucial role in the pathophysiology of Alzheimer's disease.Notably,impaired cholesterol metabolism in the liver may exacerbate the development of Alzheimer's disease.In this review,we explore the underlying causes of Alzheimer's disease and elucidate the role of the liver in amyloid-beta clearance and cholesterol metabolism.Furthermore,we propose that restoring normal cholesterol metabolism in the liver could represent a promising therapeutic strategy for addressing Alzheimer's disease.

Effect of Dangfei Liganning capsule(当飞利肝宁胶囊) on liver X receptor α/steroid regulatory element binding protein-1/fatty acid synthase signal pathway in rats with metabolic-associated fatty liver disease

OBJECTIVE: To study the mechanism of Dangfei Liganning capsule(当飞利肝宁胶囊) in the treatment of rats with metabolic associated fatty liver disease(MAFLD). METHODS: Totally 48 specific pathogen free SpragueDawley male rats were randomly divided into normal Group, model group, Dangfei Liganning high, moderate, and low-dose groups and Essentiale group which were fed with high fat diet for 8 weeks, and gavage and molding were carried out simultaneously. Dangfei Liganning high, middle and low-dose group were given 0.27, 0.135 and 0.0675 g·kg-1·d-1 respectively by gavage, Essentiale group was given 0.123 g·kg-1·d-1 by gavage, the same amount of distilled water was given by gavage in the normal group and the model group. The rats were weighed at the 0th week, 2nd week, 4th week, 6th week and 8th weekend respectively. The rats were sacrificed at the end of the 8th week. Serum levels of alanine aminotransferase(ALT), alanine aminotransferase(AST),triglyceride(TG), total cholesterol(CHO), high-density lipoprotein cholesterol(HDL-C), low-density lipoprotein (LDL-C), total protein(TP), albumin(Alb), globulin(GLB), total bilirubin(TBIL), direct bilirubin(DBIL), tumor necrosis factor-α(TNF-α) and interleukin-6(IL-6) were measured. The levels of liver tumor necrosis factor-α(TNF-α), interleukin-6(IL-6) and liver pathology [hematoxylin and eosin(HE) staining, oil red O staining] were detected. The expression levels of liver X receptor α(LXRα), steroid regulatory element binding protein-1(SREBP-1) and fatty acid synthase(FAS) were detected by immunohistochemistry, Western blot and reverse transcription-polymerase chain reaction reverse transcription-polymerase chain reaction. RESULTS: From the beginning to the 8th week, the growth rate of body weight in the Dangfei Liganning highdose group was slower than all other groups. There was no significant difference in ALB level in all groups(P > 0.05). Compared with the model group, the levels of ALT, AST, LDL-C, TG, CHO, TP, GLB, TBIL, DBIL, IL-6, TNF-α were significantly decreased and HDL-C were significantly increased in Dangfei Liganning high-dose group(P < 0.01, < 0.05). HE and oil red O staining showed that the fatty lesions in rat liver were alleviated, while the expressions of LXRα, SREBP-1, FAS m RNA and protein were significantly decreased(P < 0.01). CONCLUSIONS: Dangfei Liganning capsule can slow down the increase of body weight of MAFLD rats, reduce the levels of transaminase, Lipid and inflammatory factors in MAFLD rats, promote the synthesis of liver protein and bile metabolism, and improve the liver fatty lesion of MAFLD rats, among which the Dangfei Liganning highdose group is more effective. The mechanism of action may be through blocking LXR-SREBP-1-FAS signal pathway.

ATF4/TXNIP/REDD1/mTOR signaling mediates the antitumor activities of liver X receptor in pancreatic cancers

Background:Limited by difficulties in early detection and availabilities of effective treatments,pancreatic cancer is a highly malignant disease with poor prognosis.Nuclear receptors are a family of ligand‐dependent transcription factors that are highly druggable therapeutic targets playing critical roles in human physiological and pathological development,including cancer.In this study,we explored the therapeutic potential as well as the molecular mechanisms of liver X receptor(LXR)agonist GW3965 in pancreatic cancer.Methods:Soft‐agar colony formation assay,xenograft tumors,Oligonucleotide microarray,Reverse transcription real‐time polymerase chain reaction,Western immunoblotting and Immunohistochemistry were used in this study.Results:We demonstrated pleotropic in vitro activities of GW3965 in pancreatic cell lines MIA PaCa‐2 and BXPC3 including reduction of cell viability,inhibition of cell proliferation,stimulation of cell death,and suppression of colony formation,which translated to significant inhibition of xenograft tumor growth in vitro.By mapping the gene expression profiles,we identified the up‐regulations of 188 and the down‐regulations of 92 genes common to both cell lines following GW3965 treatment.Genes responsive to GW3965 represent a variety of biological pathways vital for multiple cellular functions.Specifically,we identified that the activating transcription factor 4/thioredoxin‐interacting protein/regulated in development and DNA damage responses 1/mechanistic target of rapamycin(ATF4/TXNIP/REDD1/mTOR)signaling critically controls GW3965‐mediated regulation of cell proliferation/death.The significance of the ATF4/TXNIP/REDD1/mTOR pathway was further supported by associated expressions in xenograft tumors as well as human pancreatic cancer samples.Conclusions:This study provides the pre‐clinical evidence that LXR agonist is a promising therapy for pancreatic cancer.

Newly-found functions of metformin for the prevention and treatment of age-related macular degeneration

Metformin(MET),a first-line oral agent used to treat diabetes,exerts its function mainly by activating adenosine monophosphate-activated protein.The accumulation of oxidized phospholipids in the outer layer of the retina plays a key role in retinal pigment epithelium(RPE)cells death and the formation of choroidal neovascularization(CNV),which mean the development of age-related macular degeneration(AMD).Recent studies have shown that MET can regulate lipid metabolism,inhibit inflammation,and prohibit retinal cell death and CNV formation due to various pathological factors.Here,newly discovered functions of MET that may be used for the prevention and treatment of AMD were reviewed.

Nuclear receptors and non-alcoholic fatty liver disease:An update

Non-alcoholic fatty liver disease(NAFLD)has become the leading cause of chronic liver disease in adults and children worldwide.The symptoms of NAFLD range from simple steatosis and non-alcoholic stea-tohepatitis(NASH)to hepatic fibrosis or cirrhosis,even ultimately develops to hepatocellular carcinoma.Nuclear receptors(NRs)are a superfamily of ligand-activated transcription factors,most of which are ligand-activated that control cellular homeostasis in the liver and other tissues.A growing number of studies demonstrated the important role of NRs in NAFLD.In this review,the current findings on the role of NRs in NAFLD are summarized and future perspectives to target NRs for NAFLD are discussed.

Effect of Quercetin on Atherosclerosis Based on Expressions of ABCA1, LXR-α and PCSK9 in ApoE-/- Mice

Objective:To investigate the effect of quercetin on ATP binding cassette transporter A1(ABCA1),liver X receptor(LXR),and proprotein convertase subtilisin/kexin type 9(PCSK9)expressions in apoE-knockout(ApoE-/-)mice.Methods:The high-fat diet-induced atherosclerosis(AS)in ApoE-/-mice was established.Thirtysix mice were divided into 3 groups using random number table method:model group(n=12),quercetin group(n=12),and atorvastatin group(n=12),with C57BL/6J mice of the same strain and age as the control group(n=12).Quercetin group and atorvastatin group were administrated with quercetin and atorvastatin by oral gavage,with doses of 12.5 and 4 mg/(kg・d),respectively.Animals in the control and model groups were given an equal volume of distilled water by oral gavage once per day for a total of 12 weeks.Western blot and immunohistochemical methods were employed to determine the aortic ABCA1,LXR-a and PCSK9 protein expressi on.En zyme linked imm uno sorbent assay method was used to detect the expressi on of serum total cholesterol(TC),triglyceride(TG),high density lipoprotein-cholesterol(HDL-C),low density lipoproteincholesterol(LDL-C),tumor necrosis factor-a(TNF-a),interleukin-6(IL-6),and IL-10,combined with tissue pathological exami nation.Results:ApoE-/-mice fed with a high-fat diet had no table atherosclerosis lesions,with reduced ABCA1,LXR-a and IL-10 levels(all P<0.01),elevated PCSK9,TNF-a and IL-6 expression,and increased TC and LDL-C con tents(all P<0.01).After querceti n in terventi on,the areas of AS plaques and the expressions of PCSK9,TNF-a and IL-6 were significantly reduced(all P<0.01),while the expressions of ABCA1 and LXR-a were increased significantly(all P<0.01).Conclusion:Quercetin effectively interfered with AS development by regulating the expressions of ABCA1,LXR-a and PCSK9 in ApoE,mice.

Transgenic overexpression of steroid sulfatase alleviates cholestasis

Background and Aim:Sulfotransferase(SULT)-mediated sulfation and steroid sulfatase(STS)-mediated desulfation represent two critical mechanisms that regulate the chemical and functional homeostasis of endogenous and exogenous molecules.STS catalyzes the hydrolysis of steroid sulfates to form hydroxysteroids.Oxygenated cholesterol derivative oxysterols are known to be endogenous ligands of the liver X receptor(LXR),a nuclear receptor with anti-cholestasis activity,whereas the sulfated oxysterols antagonize LXR signaling.The conversion of sulfated oxysterols to their non-sulfated counterparts is catalyzed by STS.The aim of this study is to determine whether STS can alleviate cholestasis by increasing the activity of LXR.Methods:Liver-specific STS transgenic mice were created and subject to the lithocholic acid(LCA)-induced model of cholestasis.Results:Transgenic overexpression of STS in the liver promoted bile acid elimination and alleviated LCAinduced cholestasis.The protective effect of the STS transgene was associated with the activation of LXR and induction of LXR target genes,likely because of the increased conversion of the antagonistic oxysterol sulfates to the agonistic oxysterols.Conclusions:STS has a novel function in controlling the homeostasis of bile acids by regulating endogenous LXR ligands.

Remembering your A, B, C’s: Alzheimer’s disease and ABCA1

The function of ATP binding cassette protein A1(ABCA1)is central to cholesterol mobilization.Reduced ABCA1 expression or activity is implicated in Alzheimer’s disease(AD)and other disorders.Therapeutic approaches to boost ABCA1 activity have yet to be translated successfully to the clinic.The risk factors for AD development and progression,including comorbid disorders such as type2 diabetes and cardiovascular disease,highlight the intersection of cholesterol transport and inflammation.Upregulation of ABCA1 can positively impact APOE lipidation,insulin sensitivity,peripheral vascular and blood-brain barrier integrity,and anti-inflammatory signaling.Various strategies towards ABCA1-boosting compounds have been described,with a bias toward nuclear hormone receptor(NHR)agonists.These agonists display beneficial preclinical effects;however,important side effects have limited development.In particular,ligands that bind liver X receptor(LXR),the primary NHR that controls ABCA1 expression,have shown positive effects in AD mouse models;however,lipogenesis and unwanted increases in triglyceride production are often observed.The longstanding approach,focusing on LXRβvs.LXRa selectivity,is over-simplistic and has failed.Novel approaches such as phenotypic screening may lead to small molecule NHR modulators that elevate ABCA1 function without inducing lipogenesis and are clinically translatable.

Alzheimer’s disease:Risk factors and therapeutic targets

Alzheimer’s disease(AD),a neurodegenerative disorder,has been determined as an outcome of genetic as well as behavioral conditions.The complete understanding of its generation and progress is yet to be understood.However,there has been a significant progress in the diagnosis and identification of the associated risk factors of AD.Several of the risk factors were found connected with cholesterol.Scientists are mainly focusing on the reduction of amyloid β and stabilization of tau protein towards the development of its drugs.To modulate amyloid β,the key components of cholesterol metabolism have been attractive targets and the enzymes involved in the phosphorylation of tau have been tried to stabilize tau protein.This review article briefly highlights the symptoms,risk factors,and drug targets of AD.