Developmental and extrahepatic physiological functions of SREBP pathway genes in mice

Protective effect of curcumin against endoplasmic reticulum stress and lipid metabolism disorders in AFB1-intoxicated duck liver

Aflatoxin B1 (AFB1) is a stable and highly toxic toxin that causes multi-organ toxicity with sustained ingestion, most typically in the duck liver. Previous research has shown that AFB1 can bring about endoplasmic reticulum stress (ERS) in animals, and ERS is strongly associated with lipid metabolism. However, the relationship between AFB1-induced duck liver toxicity and ERS and lipid metabolism is currently unclear. Great attention has been paid to the prevention and treatment of AFB1 because of its great harm. Curcumin, a natural polyphenol, is notable for its powerful anti-inflammatory and antioxidant properties. Studies have shown curcumin to be protective against afb1-induced avian multi-organ toxicity. However, the effects of curcumin on the liver of ducks exposed to AFB1 are largely unknown. In the present study, we aimed to investigate whether AFB1 exposure induces ERS and lipid metabolism disorders in duck liver, while exploring the positive role of curcumin in it. One-day-old ducks (n = 80) were randomly divided in four groups: control group, AFB1 group (0.1 mg / kg.bw AFB1), Cur group (400 mg/kg curcumin), and AFB1 + Cur group (0.1 mg/kg.bw AFB1 + 400 mg/kg curcumin), and blood and liver were collected for the study after 21 days of continuous administration. Our research has found that AFB1 exposure significantly increases the levels of liver function indicators ALP, AST, and ALT in ducks' serum (P < 0.05). Duck liver undergoes fatty degeneration under the influence of AFB1. Under the effect of curcumin, AFB1-induced structural damage in duck liver was somewhat controlled. Further experimental results showed that AFB1 treatment significantly increased the expression of glucose-regulated protein 78 (P < 0.001), and activated the endoplasmic reticulum stress pathway. Meanwhile, AFB1 inhibited the LKB1-AMPK signaling pathway and disrupted lipid metabolic homeostasis. And curcumin treatment effectively reversed these changes. Overall, our results suggest that curcumin attenuates AFB1-induced hepatotoxicity in ducks by inhibiting ERS and lipid metabolism disorders.

Inhibition of MBTPS1 enhances antitumor immunity and potentiates anti-PD-1 immunotherapy

Despite advances in cancer immunotherapy, colorectal cancer patients exhibit limited therapeutic responses. Therefore, the exploration of strategies combining immunotherapy with adjuvant approaches to enhance adaptive immune responses is in demand. Here, we perform a customized in vivo CRISPR-Cas9 screen to target genes encoding membrane and secreted proteins in CRC mouse models with different immune characteristics. We observe that loss of membrane-bound transcription factor site-1 protease (MBTPS1) in tumor cells enhances antitumor immunity and potentiates anti-PD-1 therapy. Mechanistic studies reveal that tumor cell-intrinsic MBTPS1 competes with USP13 for binding to STAT1, thereby disrupting the USP13-dependent deubiquitination-mediated STAT1 stabilization. The upregulated STAT1-transcribed chemokines including CXCL9, CXCL10, and CXCL11, promote CXCR3+CD8+ T cell infiltration. Notably, the regulatory role of MBTPS1 in antitumor immunity operates independently of its classic function in cleaving membrane-bound transcription factors. Collectively, our results provide a theoretical basis for MBTPS1 as a potential immunotherapy target.

HIV-TAT dysregulates microglial lipid metabolism through SREBP2/miR-124 axis: Implication of lipid droplet accumulation microglia in NeuroHIV

Chronic HIV infection can dysregulate lipid/cholesterol metabolism in the peripheral system, contributing to the higher incidences of diabetes and atherosclerosis in HIV (+) individuals. Recently, accumulating evidence indicate that HIV proteins can also dysregulate lipid/cholesterol metabolism in the brain and such dysregulation could be linked with the pathogenesis of HIV-associated neurological disorders (HAND)/NeuroHIV. To further characterize the association between lipid/cholesterol metabolism and HAND, we employed HIV-inducible transactivator of transcription (iTAT) and control mice to compare their brain lipid profiles. Our results reveal that HIV-iTAT mice possess dysregulated lipid profiles and have increased numbers of lipid droplets (LDs) accumulation microglia (LDAM) in the brains. HIV protein TAT can upregulate LDs formation through enhancing the lipid/cholesterol synthesis in vitro. Mechanistically, HIV-TAT increases the expression of sterol regulatory element-binding protein 2 (SREBP2) through microRNA-124 downregulation. Cholesterol synthesis inhibition can block HIV-TAT-mediated NLRP3 inflammasome activation and microglial activation in vitro as well as mitigate aging-related behavioral impairment and memory deficiency in HIV-iTAT mice. Taken together, our results indicate an inherent role of lipid metabolism and LDAM in the pathogenesis of NeuroHIV (immunometabolism). These findings suggest that LDAM reversal through modulating lipid/cholesterol metabolism could be a novel therapeutic target for ameliorating NeuroHIV symptoms in chronic HIV (+) individuals.

Deciphering the Role of the SREBF1 Gene in the Transcriptional Regulation of Porcine Adipogenesis Using CRISPR/Cas9 Editing

Sterol regulatory element-binding protein 1 (SREBP1) is an important transcription factor that controls lipid metabolism and adipogenesis. Two isoforms, SREBP1a and SREBP1c, are generated by alternative splicing of the first exon of the SREBF1 gene. The porcine SREBF1 gene has mainly been studied for its role in lipid metabolism in adipose tissues, but little is known about its involvement, and the role of its two isoforms, in adipogenesis. The aim of the present study was to introduce a deletion in the 5'-regulatory region of the SREBF1c gene, considered crucial for adipogenesis, using the Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR-associated protein 9 (CRISPR/Cas9) method. This approach allows for the evaluation of how inhibiting SREBF1c transcription affects the expression of other genes essential for adipocyte differentiation, particularly PPARG, CEBPA, CEBPB, CEBPD, GATA2, and FABP4. It was observed that disrupting the SREBF1c isoform had no effect on the GATA2 gene but did result in a decrease in the expression of the CEBPA and CEBPD genes, an increase in the expression of CEBPB, and an inhibition in the expression of the PPARG and FABP4 genes. These changes in gene expression blocked adipogenesis, as could be seen by the failure of lipid droplets to accumulate. Our results provide evidence highlighting the pivotal role of the SREBP1c isoform in the regulation of porcine adipogenesis.

Zhimu-Huangbai herb-pair ameliorates hepatic steatosis in mice by regulating IRE1α/XBP1s pathway to inhibit SREBP-1c

BACKGROUND

Currently, there is a lack of validated pharmacological interventions for non-alcoholic fatty liver disease (NAFLD), which is characterized by the accumulation of hepatic triglyceride. Zhimu-Huangbai (ZH) herb-pair is a traditional Chinese medicine that regulates glucose and lipid metabolism disorders. However, the precise mechanisms underlying the preventive effects of hepatic triglyceride induced by high-fat diet (HFD) remain elusive.

PURPOSE

The study aimed to examine the impact of ZH herb-pair on NAFLD in mice and explore the underlying mechanisms, particularly its effects on endoplasmic reticulum (ER) stress and lipid metabolism.

METHODS

NAFLD was induced in mice using HFD, and the treated mice were orally administered ZH, metformin (Glucophage) or lovastatin. The lipid metabolism factors, ER stress markers, and the unfolded protein response (UPR) branch factors were measured using immunohistochemistry, western blotting or qRT-PCR. Co-Immunoprecipitation (CoIP) was performed to reveal the connection between SCAP and SREBP-1c. Tunicamycin (TM) and plasmid delivery were used to induce acute ER stress or crease XBP1 gain function models. The main compounds in ZH binding to IRE1α protein were studied by molecular docking and cellular thermal shift assay (CETSA).

RESULTS

Treatment with ZH significantly ameliorated hepatic steatosis and reduced lipid synthesis process mainly inhibiting the expression of mature active form of SREBP-1c through relieving ER stress. The expression of IRE1α and XBP1s was inhibited after treatment with ZH. In addition, ZH improved the fatty liver phenotype caused by XBP1 overexpression via decreasing srebp1c transcription. In vitro experimental results suggested that the main compounds in ZH decreased cellular TG contents. Mechanistically, ZH targeted IRE1α and inhibited XBP1s mRNA expression to relieve ER stress and inhibit SREBP-1c production.

CONCLUSIONS

ZH herb-pair can protect against NAFLD by reducing the expression of SREBP-1c, in part, via regulating IRE1α/XBP1s pathway.

Bergenin, the main active ingredient of Bergenia purpurascens, attenuates Th17 cell differentiation by downregulating fatty acid synthesis

Bergenin is the main active ingredient of Bergenia purpurascens, a medicinal plant which has long been used to treat a variety of Th17 cell-related diseases in China, such as allergic airway inflammation and colitis. This study aimed to uncover the underlying mechanisms by which bergenin impedes Th17 cell response in view of cellular metabolism. In vitro, bergenin treatment reduced the frequency of Th17 cells generated from naïve CD4+ T cells of mice. Mechanistically, bergenin preferentially restrained fatty acid synthesis (FAS) but not other metabolic pathways in differentiating Th17 cells, and exogenous addition of either palmitic acid (PA) or oleic acid (OA) and combination with acetyl-CoA carboxylase 1 (ACC1) activator citric acid dampened the inhibition of bergenin on Th17 cell differentiation. Bergenin inhibited FAS through downregulating the expression of SREBP1 via restriction of histone H3K27 acetylation in the SREBP1 promoter, and SREBP1 overexpression weakened the inhibition of bergenin on Th17 differentiation. Furthermore, bergenin was shown to directly interact with SIRT1 and result in activation of SIRT1. Either combination with SIRT1 inhibitor EX527 or point mutation plasmid of SIRT1 diminished the inhibitory effect of bergenin on FAS and Th17 cell differentiation. Finally, the inhibitory effect of bergenin on Th17 cell response and SIRT1 dependence were verified in mice with dextran sulfate sodium-induced colitis. In short, bergenin repressed Th17 cell response by downregulating FAS via activation of SIRT1, which might find therapeutic use in Th17 cell-related diseases.

SREBP-Dependent Regulation of Lipid Homeostasis Is Required for Progression and Growth of Pancreatic Ductal Adenocarcinoma

Solid tumors undergo metabolic reprogramming when growth outstrips local nutrient supply. Lipids such as cholesterol and fatty acids are required for continued tumor cell proliferation, and oncogenic mutations stimulate de novo lipogenesis to support tumor growth. Sterol regulatory element-binding protein (SREBP) transcription factors control lipid homeostasis by activating genes required for lipid synthesis and uptake. SREBPs have been implicated in the progression of brain, breast, colon, liver, and prostate cancers. However, the role of the SREBP pathway and its central regulator SREBP cleavage activating protein (SCAP) in pancreatic ductal adenocarcinoma (PDAC) has not been studied in detail. Here, we demonstrated that pancreas-specific knockout of Scap has no effect on mouse pancreas development or function, allowing for examination of the role of Scap in the murine KPC model of PDAC. Notably, heterozygous loss of Scap prolonged survival in KPC mice, and homozygous loss of Scap impaired PDAC tumor progression. Using xenograft models, we showed that SCAP is required for human PDAC tumor growth. Mechanistically, chemical or genetic inhibition of the SREBP pathway prevented PDAC cell growth under low-serum conditions because of a lack of lipid supply. Highlighting its clinical importance, the SREBP pathway is broadly required across cancer cell lines, target genes are upregulated in human PDAC tumors, and increased expression of SREBP targets is associated with poor survival in patients with PDAC. Collectively, these results demonstrate that SCAP and SREBP pathway activity are required for PDAC cell and tumor growth, identifying SCAP as a potential therapeutic target for PDAC.

SIGNIFICANCE

Our findings demonstrate that SREBP pathway activation is a critical part of the metabolic reprogramming that occurs in PDAC development and progression. Therefore, targeting the SREBP pathway has significant therapeutic potential.

SREBP-1-mediated lipogenesis confers resistance to ferroptosis and improves endothelial injury

Atherosclerosis refers to a disease characterized by the formation of lipid plaque deposits within arterial walls, leading to reduced blood flow or blockage of blood outflow. The process of endothelial injury induced by oxidized low-density lipoprotein (ox-LDL) is considered the initial stage of atherosclerosis. Ferroptosis is a form of iron-dependent, non-apoptotic cell death, and current research suggests its association with coronary artery disease (CAD). In this study, we observed a correlation between reduced expression of SREBP-1 and the occurrence of stable CAD. Additionally, during the process of endothelial injury induced by ox-LDL, we also noted decreased expression of the SREBP-1/SCD1/FADS2 and involvement in the ferroptosis process. Mechanistically, ox-LDL induced endothelial injury by inhibiting the lipid biosynthesis process mediated by the SREBP-1/SCD1/FADS2, thereby inducing lipid peroxidation and ferroptosis. On the contrary, overexpression of SREBP-1 or supplementation with monounsaturated fatty acids counteracted iron accumulation, mitochondrial damage, and lipid peroxidation-induced ferroptosis, thereby improving endothelial injury. Our study indicated that the decreased expression of peripheral blood SREBP-1 mRNA is an independent risk factor for stable CAD. Furthermore, in endothelial cells, the lipid biosynthesis process mediated by SREBP-1 could ameliorate endothelial injury by resisting ferroptosis. The study has been registered with the Chinese Clinical Trial Registry, which serves as a primary registry in the World Health Organization International Clinical Trials Registry Platform (ChiCTR2300074315, August 3rd, 2023).

Regulation and targeting of SREBP-1 in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is an increasing burden on global public health and is associated with enhanced lipogenesis, fatty acid uptake, and lipid metabolic reprogramming. De novo lipogenesis is under the control of the transcription factor sterol regulatory element-binding protein 1 (SREBP-1) and essentially contributes to HCC progression. Here, we summarize the current knowledge on the regulation of SREBP-1 isoforms in HCC based on cellular, animal, and clinical data. Specifically, we (i) address the overarching mechanisms for regulating SREBP-1 transcription, proteolytic processing, nuclear stability, and transactivation and (ii) critically discuss their impact on HCC, taking into account (iii) insights from pharmacological approaches. Emphasis is placed on cross-talk with the phosphatidylinositol-3-kinase (PI3K)-protein kinase B (Akt)-mechanistic target of rapamycin (mTOR) axis, AMP-activated protein kinase (AMPK), protein kinase A (PKA), and other kinases that directly phosphorylate SREBP-1; transcription factors, such as liver X receptor (LXR), peroxisome proliferator-activated receptors (PPARs), proliferator-activated receptor γ co-activator 1 (PGC-1), signal transducers and activators of transcription (STATs), and Myc; epigenetic mechanisms; post-translational modifications of SREBP-1; and SREBP-1-regulatory metabolites such as oxysterols and polyunsaturated fatty acids. By carefully scrutinizing the role of SREBP-1 in HCC development, progression, metastasis, and therapy resistance, we shed light on the potential of SREBP-1-targeting strategies in HCC prevention and treatment.

Lipid Droplets Accumulation in the Brain of HIV Transgenic Rat: Implication in the Accelerated Aging of HIV Infected Individuals

Abnormal microglial activation has been suggested as "driven force" promoting brain aging. Lipid droplets accumulating microglia (LDAM), identified as a novel inflammatory phenotype, elevate neuroinflammation and exaggerate neuronal injuries in aging and multiple neurodegenerative diseases. Since chronic HIV (human immunodeficiency virus) (+) individuals show an accelerated brain aging and higher incidence of neurological symptoms compared to age-matched HIV (-) population, we hypothesize that LDAM are also involved in such phenomenon. For validating the hypothesis, we employed HIV transgenic (HIV-Tg) and wilt type (WT) rats to check lipid droplets (LDs) accumulation in the brains at mature (6 months) and middle age (12 months). Our results showed that HIV-Tg rats possess higher levels of LDs formation in the hippocampus (HP) and prefrontal cortex (PFc) than controls at middle age. Increased LDs are mainly presented in microglia in the HP but largely co-localized with astrocytes in the PFc. Interestingly, increased LDs are associated with upregulation on Iba1 but not with GFAP levels. HIV-Tg rats reveal an accelerated LDs accumulation during normal aging. Purified microglia from HIV-Tg rats (12 month) show higher expression of neuroimmune signaling than microglia from controls. HIV-Tg rats showed dysregulation on cholesterol synthesis in the brain HP as well as deficiency on locomotion coordination compared to controls. Overall, our results demonstrate substantial LDs accumulation in the brains of HIV-Tg rats which is associated with abnormal microglial activation and accelerated decline on locomotion coordination during aging. Dysregulation on lipid metabolism might underlie accelerated brain aging in the context of chronic HIV infection.

SREBP-dependent regulation of lipid homeostasis is required for progression and growth of pancreatic ductal adenocarcinoma

Metabolic reprogramming is a necessary component of oncogenesis and cancer progression that solid tumors undergo when their growth outstrips local nutrient supply. The supply of lipids such as cholesterol and fatty acids is required for continued tumor cell proliferation, and oncogenic mutations stimulate de novo lipogenesis to support tumor growth. Sterol regulatory element-binding protein (SREBP) transcription factors control cellular lipid homeostasis by activating genes required for lipid synthesis and uptake. SREBPs have been implicated in the progression of multiple cancers, including brain, breast, colon, liver, and prostate. However, the role the SREBP pathway and its central regulator SREBP cleavage activating protein (SCAP) in pancreatic ductal adenocarcinoma (PDAC) has not been studied in detail. Here, we demonstrated that pancreas-specific knockout of Scap has no effect on mouse pancreas development or function, allowing for examination of the role for Scap in the murine KPC model of PDAC. Notably, heterozygous loss of Scap prolonged survival in KPC mice, and homozygous loss of Scap impaired PDAC tumor progression. Using subcutaneous and orthotopic xenograft models, we showed that S CAP is required for human PDAC tumor growth. Mechanistically, chemical or genetic inhibition of the SREBP pathway prevented PDAC cell growth under low serum conditions due to a lack of lipid supply. Highlighting the clinical importance of this pathway, the SREBP pathway is broadly required for cancer cell growth, SREBP target genes are upregulated in human PDAC tumors, and increased expression of SREBP targets genes is associated with poor survival in PDAC patients. Collectively, these results demonstrate that SCAP and the SREBP pathway activity are essential for PDAC cell and tumor growth in vitro and in vivo , identifying SCAP as a potential therapeutic target for PDAC.

SIGNIFICANCE

Our findings demonstrate that SREBP pathway activation is a critical part of the metabolic reprogramming that occurs in PDAC development and progression. Therefore, targeting the SREBP pathway has significant therapeutic potential.

Isocaloric diets with varying protein levels affected energy metabolism in young adult Sprague-Dawley rats via modifying the gut microbes: A lipid imbalance was brought on by a diet with a particularly high protein content

Protein is the most important macro-nutrient when it comes to maximizing health, body composition, muscle growth, and recovery of body tissue. In recent years, it has been found that protein also plays an important role in metabolism and gut microbiota. This study was performed to investigate the effects of an isocaloric diet with different crude protein contents on the energy metabolism of Sprague-Dawley (SD) rats. Results revealed that compared with the 20% crude protein (CP; control) diet, the 38% CP diet improved serum parameters that are associated with dyslipidemia and glucose metabolic disorders in SD rats, whereas the 50% CP diet increased liver injury indicators and fatty acid synthesis-related genes and protein expression in the liver. Compared with the control diet, the 14% CP diet increased the abundance of colonic short-chain fatty acid-producing bacteria (Lachnospiraceae_NK4A136_group and Ruminiclostridium_9) and promoted colonic microbial cysteine and methionine metabolism, the 38% CP diet up-regulated colonic microbial lysine biosynthesis and degradation pathways, and the 50% CP diet down-regulated colonic mucosal cholesterol metabolism. Furthermore, the increase of multiple colonic enteropathogenic bacteria in the 50% CP group was associated with higher palmitic acid and stearic acid concentrations in the colonic microbes and lower cholesterol and arachidonic acid concentrations in the colonic mucosa. These findings revealed that the 14% CP and 38% CP diets improved rats' energy metabolism, while the 50% CP diet was accompanied by lipid metabolism imbalances and an increase in the abundance of multiple enteropathogenic bacteria.

Ganoderma lucidum polysaccharide ameliorates cholesterol gallstone formation by modulating cholesterol and bile acid metabolism in an FXR-dependent manner

BACKGROUND

Cholesterol gallstone (CG) disease is a worldwide common disease characterized by cholesterol supersaturation in gallbladder bile. Ganoderma lucidum polysaccharide (GLP) has been shown to possess various beneficial effects against metabolic disorders. However, the role and underlying mechanism of GLP in CG formation are still unknown. This study aimed to determine the role of GLP in ameliorating lithogenic diet (LD)-induced CG formation.

METHODS

Mice were fed either a normal chow diet, a LD, or LD supplemented with GLP. Real-time quantitative polymerase chain reaction (RT-qPCR) and western blotting were used to detect the expression of genes involved in cholesterol and bile acid (BA) metabolism. The BA concentrations in the ileum were quantified by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The microbiota in cecal contents were characterized using 16S ribosomal RNA (16S rRNA) gene sequencing.

RESULTS

GLP effectively alleviated CG formation induced by LD. Specifically, GLP reduced the total cholesterol (TC) levels, increased the total BA levels, and decreased the cholesterol saturation index (CSI) in gallbladder bile. The protective effect of GLP was attributed to the inhibition of farnesoid X receptor (FXR) signaling, increased hepatic BA synthesis and decreased hepatic cholesterol synthesis and secretion. GLP also altered the BA composition in the ileum, reducing FXR-agonistic BAs and increasing FXR-antagonistic BAs, which may contribute to the inhibition of intestinal FXR signaling. Additionally, GLP improved dysbiosis of the intestinal flora and reduced the serum levels of hydrogen sulfide (H2S), a bacterial metabolite that can induce hepatic FXR, thereby inhibiting hepatic FXR signaling. Moreover, the protective effect of GLP against CG formation could be reversed by both the global and gut-restricted FXR agonists.

CONCLUSIONS

Taken together, GLP ameliorates CG formation by regulating cholesterol and BA metabolism in an FXR-dependent manner. Our study demonstrates that GLP may be a potential strategy for the prevention against CG disease.

SREBPs as the potential target for solving the polypharmacy dilemma

The phenomenon of polypharmacy is a common occurrence among older people with multiple health conditions due to the rapid increase in population aging and the popularization of clinical guidelines. The prevalence of metabolic syndrome is growing quickly, representing a serious threat to both the public and the worldwide healthcare systems. In addition, it enhances the risk of cardiovascular disease as well as mortality and morbidity. Sterol regulatory element binding proteins (SREBPs) are basic helix-loop-helix leucine zipper transcription factors that transcriptionally modulate genes that regulate lipid biosynthesis and uptake, thereby serving an essential role in biological systems regulation. In this article, we have described the structure of SREBPs and explored their activation and regulation of signals. We also reveal that SREBPs are intricately involved in the modulation of metabolic diseases and thus have tremendous potential as the novel target for single-drug therapy for multiple diseases.

Luteolin as a potential hepatoprotective drug: Molecular mechanisms and treatment strategies

Luteolin is a flavonoid widely present in various traditional Chinese medicines. In recent years, luteolin has received more attention due to its impressive liver protective effect, such as metabolic associated fatty liver disease, hepatic fibrosis and hepatoma. This article summarizes the pharmacological effects, pharmacokinetic characteristics, and toxicity of luteolin against liver diseases, and provides prospect. The results indicate that luteolin improves liver lesions through various mechanisms, including inhibiting inflammatory factors, reducing oxidative stress, regulating lipid balance, slowing down excessive aggregation of extracellular matrix, inducing apoptosis and autophagy of liver cancer cells. Pharmacokinetics research manifested that due to metabolic effects, the bioavailability of luteolin is relatively low. It is worth noting that appropriate modification, new delivery systems, and derivatives can enhance its bioavailability. Although many studies have shown that the toxicity of luteolin is minimal, strict toxicity experiments are still needed to evaluate its safety and promote its reasonable development. In addition, this study also discussed the clinical applications related to luteolin, indicating that it is a key component of commonly used liver protective drugs in clinical practice. In view of its excellent pharmacological effects, luteolin is expected to become a potential drug for the treatment of various liver diseases.

Regulation of cholesterol metabolism: New players for an old physiological process

Identified more than two centuries ago, cholesterol plays a pivotal role in human physiology. Since cholesterol metabolism is a physiologically significant process, it is not surprising that its alterations are associated with several pathologies. The discovery of new molecular targets or compounds able to modulate this sophisticated metabolism has been capturing the attention of research groups worldwide since many years. Endogenous and exogenous compounds are known to regulate cellular cholesterol synthesis and uptake, or reduce cholesterol absorption at the intestinal level, thereby regulating cholesterol homeostasis. However, there is a great need of new modulators and diverse new pathways have been uncovered. Here, after illustrating cholesterol metabolism and its well-known regulators, some new players of this important physiological process are also described.

Novel wine in an old bottle: Preventive and therapeutic potentials of andrographolide in atherosclerotic cardiovascular diseases

Atherosclerotic cardiovascular disease (ASCVD) frequently results in sudden death and poses a serious threat to public health worldwide. The drugs approved for the prevention and treatment of ASCVD are usually used in combination but are inefficient owing to their side effects and single therapeutic targets. Therefore, the use of natural products in developing drugs for the prevention and treatment of ASCVD has received great scholarly attention. Andrographolide (AG) is a diterpenoid lactone compound extracted from Andrographis paniculata. In addition to its use in conditions such as sore throat, AG can be used to prevent and treat ASCVD. It is different from drugs that are commonly used in the prevention and treatment of ASCVD and can not only treat obesity, diabetes, hyperlipidaemia and ASCVD but also inhibit the pathological process of atherosclerosis (AS) including lipid accumulation, inflammation, oxidative stress and cellular abnormalities by regulating various targets and pathways. However, the pharmacological mechanisms of AG underlying the prevention and treatment of ASCVD have not been corroborated, which may hinder its clinical development and application. Therefore, this review summarizes the physiological and pathological mechanisms underlying the development of ASCVD and the in vivo and in vitro pharmacological effects of AG on the relative risk factors of AS and ASCVD. The findings support the use of the old pharmacological compound ('old bottle') as a novel drug ('novel wine') for the prevention and treatment of ASCVD. Additionally, this review summarizes studies on the availability as well as pharmaceutical and pharmacokinetic properties of AG, aiming to provide more information regarding the clinical application and further research and development of AG.

Docosahexaenoic Acid Alters Lipid Metabolism Processes via H3K9ac Epigenetic Modification in Dairy Goat

Goat milk is increasingly recognized by consumers due to its high nutritional value, richness in short- and medium-chain fatty acids, and richness in polyunsaturated fatty acids (PUFA). Exogenous supplementation of docosahexaenoic acid (DHA) is an important approach to increasing the content of PUFA in goat milk. Several studies have reported benefits of dietary DHA in terms of human health, including potential against chronic diseases and tumors. However, the mechanisms whereby an increased supply of DHA regulates mammary cell function is unknown. In this study, we investigated the effect of DHA on lipid metabolism processes in goat mammary epithelial cells (GMEC) and the function of H3K9ac epigenetic modifications in this process. Supplementation of DHA promoted lipid droplet accumulation increased the DHA content and altered fatty acid composition in GMEC. Lipid metabolism processes were altered by DHA supplementation through transcriptional programs in GMEC. ChIP-seq analysis revealed that DHA induced genome-wide H3K9ac epigenetic changes in GMEC. Multiomics analyses (H3K9ac genome-wide screening and RNA-seq) revealed that DHA-induced expression of lipid metabolism genes (FASN, SCD1, FADS1, FADS2, LPIN1, DGAT1, MBOAT2), which were closely related with changes in lipid metabolism processes and fatty acid profiles, were regulated by modification of H3K9ac. In particular, DHA increased the enrichment of H3K9ac in the promoter region of PDK4 and promoted its transcription, while PDK4 inhibited lipid synthesis and activated AMPK signaling in GMEC. The activation of the expression of fatty acid metabolism-related genes FASN, FADS2, and SCD1 and their upstream transcription factor SREBP1 by the AMPK inhibitor was attenuated in PDK4-overexpressing GMEC. In conclusion, DHA alters lipid metabolism processes via H3K9ac modifications and the PDK4-AMPK-SREBP1 signaling axis in goat mammary epithelial cells, providing new insights into the mechanism through which DHA affects mammary cell function and regulates milk fat metabolism.

SCAP contributes to embryonic angiogenesis by negatively regulating KISS-1 expression in mice

Sterol regulatory element-binding protein (SREBP) cleavage-activating protein (SCAP) is indispensable in organ development because it maintains intracellular cholesterol homeostasis. The vessel is not widely conceived of as a cholesterol-sensitive tissue, so the specific role of SCAP in angiogenesis has not been paid attention to. As an important component of the vascular mesoderm, vascular smooth muscle cells (VSMCs) are widely involved in each step of angiogenesis. Here, we report for the first time that VSMC-specific ablation of SCAP inhibits VSMC proliferation and migration, interacting with endothelial cells (ECs), and finally causes defective embryonic angiogenesis in mice. Mechanistically, we demonstrated that SCAP ablation in VSMCs leads to the upregulation of KISS-1 protein, consequently resulting in suppressed activation of the MAPK/ERK signaling pathway and downregulation of matrix metalloproteinase 9 (MMP9) and vascular endothelial-derived growth factor (VEGF) expression to prevent angiogenesis. Importantly, we found that SCAP promotes the cleavage and nuclear translocation of SREBP2, which acts as a negative transcription regulator, regulating KISS-1 expression. Our findings suggest that SCAP contributes to embryonic angiogenesis by negatively regulating KISS-1 expression in mice and provide a new point of view for therapeutic targets of vascular development.

SCAP deficiency facilitates obesity and insulin resistance through shifting adipose tissue macrophage polarization

INTRODUCTION

Sterol regulatory element binding protein (SREBP) cleavage-associating protein (SCAP) is a sterol-regulated escort protein that translocates SREBPs from the endoplasmic reticulum to the Golgi apparatus, thereby activating lipid metabolism and cholesterol synthesis. Although SCAP regulates lipid metabolism in metabolic tissues, such as the liver and muscle, the effect of macrophage-specific SCAP deficiency in adipose tissue macrophages (ATMs) of patients with metabolic diseases is not completely understood.

OBJECTIVES

Here, we examined the function of SCAP in high-fat/high-sucrose diet (HFHS)-fed mice and investigated its role in the polarization of classical activated macrophages in adipose tissue.

METHODS

Macrophage-specific SCAP knockout (mKO) mice were generated through crossbreeding lysozyme 2-cre mice with SCAP floxed mice which were then fed HFHS for 12 weeks. Primary macrophages were derived from bone marrow cells and analyzed further.

RESULTS

We found that fat accumulation and the appearance of proinflammatory M1 macrophages were both higher in HFHS-fed SCAP mKO mice relative to floxed control mice. We traced the effect to a defect in the lipopolysaccharide-mediated increase in SREBP-1a that occurs in control but not SCAP mKO mice. Mechanistically, SREBP-1a increased expression of cholesterol 25-hydroxylase transcription, resulting in an increase in the production of 25-hydroxycholesterol (25-HC), an endogenous agonist of liver X receptor alpha (LXRα) which increased expression of cholesterol efflux to limit cholesterol accumulation and M1 polarization. In the absence of SCAP mediated activation of SREBP-1a, increased M1 macrophage polarization resulted in reduced cholesterol efflux downstream from 25-HC-dependent LXRα activation.

CONCLUSION

Overall, the activation of the SCAP-SREBP-1a pathway in macrophages may provide a novel therapeutic strategy that ameliorates obesity by controlling cholesterol homeostasis in ATMs.

Non-Esterified Fatty Acid-Induced Apoptosis in Bovine Granulosa Cells via ROS-Activated PI3K/AKT/FoxO1 Pathway

Non-esterified fatty acid (NEFA), one of negative energy balance (NEB)'s most well-known products, has a significant impact on cows' reproductive potential. Our study used an in vitro model to investigate the deleterious effects of NEFA on bovine granulosa cells (BGCs) and its underlying molecular mechanism. The results showed that high levels of NEFA led to the accumulation of reactive oxygen species (ROS), increased the expression of apoptosis-related factors such as Bcl2-Associated X/B-cell lymphoma-2 (Bax/Bcl-2) and Caspase-3, and down-regulated steroid synthesis-related genes such as sterol regulatory element binding protein 1 (SREBP-1), cytochrome P450c17 (CYP17), and cytochrome P450 aromatase (CYP19), to promote oxidative stress, cell apoptosis, and steroid hormone synthesis disorders in BGCs. In addition, NEFA significantly inhibited phosphatidylinositol 3-kinase (PI3K) and phosphorylated protein kinase B (p-AKT) activity and increased forkhead box O1 (FoxO1) expression. To further explore the role of the PI3K/AKT/FoxO1 signaling pathway in NEFA, we found that pretreatment with AKT-specific activator SC79 (5 mg/mL) for 2 h or transfection with FoxO1 knockdown siRNA in BGCs could alleviate the negative effects of NEFA treatment by decreasing Bax/Bcl-2 ratio and Caspase-3 expression, and upregulating SREBP-1, CYP17, and CYP19 expression. Meanwhile, SC79 significantly inhibited NEFA-induced dephosphorylation and massive nuclear translocation of FoxO1. Taken together, the NEFA induced oxidative stress, apoptosis, and steroid hormone synthesis disorders in BGCs by inhibiting the PI3K/AKT pathway that regulates FoxO1 phosphorylation and nuclear translocation. Our findings help to clarify the molecular mechanisms underlying the negative effects of high levels of NEFA on BGCs.

Goat FADS2 controlling fatty acid metabolism is directly regulated by SREBP1 in mammary epithelial cells

Goat milk provides benefits to human health due to its richness in bioactive components, such as polyunsaturated fatty acids (PUFAs). The fatty acid desaturase 2 (FADS2) is the first rate-limiting enzyme in PUFAs biosynthesis. However, its role and transcriptional regulation mechanisms in fatty acid metabolism in dairy goat remain unclear. Here, our study revealed that the FADS2 gene was highly expressed during the peak lactation compared with the dry period, early lactation, and late lactation. The content of triacylglycerol (TAG) was enhanced with the increasing mRNA expression of TAG synthesis genes (diacylglycerol acyltransferase 1/2, DGAT1/2) in FADS2-overexpressed goat mammary epithelial cells (GMECs). Overexpression of FADS2 was positively correlated with the elevated concentrations of dihomo-gamma-linolenic acid (DGLA) and docosahexaenoic acid (DHA) in GMECs. BODIPY staining showed that FADS2 promoted lipid droplet accumulation in GMECs. To clarify the transcriptional regulatory mechanisms of FADS2, 2,226 bp length of FADS2 promoter was obtained. Deletion mutation assays revealed that the core region of FADS2 promoter was located between the -375 and -26 region, which contained SRE1 (-361/-351) and SRE2 (-191/-181) cis-acting elements of transcription factor sterol regulatory element-binding protein 1 (SREBP1). Overexpression of SREBP1 enhanced relative luciferase activity of the single mutant of SRE1 or SRE2, vice versa, and failed to alter the relative luciferase activity of the joint mutant of SRE1 and SRE2. Chromatin immunoprecipitation (ChIP) and site-directed mutation assays further demonstrated that SREBP1 regulated the transcription of the FADS2 gene by binding to SRE sites in vivo and in vitro. In addition, the mRNA levels of FADS2 were significantly decreased by targeting SRE1 and SRE2 sites in the genome via the CRISPR interference (CRISPRi) system. These findings establish a direct role for FADS2 regulating TAG and fatty acid synthesis by SREBP1 transcriptional regulation in dairy goat, providing new insights into fatty acid metabolism in mammary gland of ruminants.

Cholesterol dyshomeostasis in amyotrophic lateral sclerosis: cause, consequence, or epiphenomenon?

Amyotrophic lateral sclerosis (ALS), the most common adult-onset motor neuron disease, is characterized by the selective degeneration of motor neurons leading to paralysis and eventual death. Multiple pathogenic mechanisms, including systemic dysmetabolism, have been proposed to contribute to ALS. Among them, dyslipidemia, i.e., abnormal level of cholesterol and other lipids in the circulation and central nervous system (CNS), has been reported in ALS patients, but without a consensus. Cholesterol is a constituent of cellular membranes and a precursor of steroid hormones, oxysterols, and bile acids. Consequently, optimal cholesterol levels are essential for health. Due to the blood-brain barrier (BBB), cholesterol cannot move between the CNS and the rest of the body. As such, cholesterol metabolism in the CNS is proposed to operate autonomously. Despite its importance, it remains elusive how cholesterol dyshomeostasis may contribute to ALS. In this review, we aim to describe the current state of cholesterol metabolism research in ALS, identify unresolved issues, and provide potential directions.

Effects of protein intake from an energy-restricted diet on the skeletal muscle composition of overweight and obese rats

Excess weight and obesity are often associated with ectopic adipose tissue accumulation in skeletal muscles. Intermuscular adipose tissue (IMAT) impairs muscle quality and reduces insulin-stimulated skeletal muscle glucose uptake. Although energy restriction and high protein intake can decrease IMAT, the effects and mechanisms of protein intake from an energy-restricted diet on protein and fat masses in skeletal muscle have received little attention. After establishing a diet-induced overweight and obese Sprague-Dawley rat model (half male and half female), rats were divided into five groups: normal control (NC; normal weight, general maintenance diet), model control (MC; overweight and obesity, high-fat diet), energy-restricted low protein (LP; overweight and obesity, 60% energy intake of NC, general maintenance diet), energy-restricted normal protein (NP; overweight and obesity, 60% energy intake of NC, high-protein diet 1), and energy-restricted high protein (HP; overweight and obesity, 60% energy intake of NC, high-protein diet 2). After 8 weeks, plasma and skeletal muscle (quadriceps femoris and gastrocnemius) samples were collected. Plasma levels of glucose, triglycerides, and hormones were analyzed, while contents of protein, fat, and factors associated with their synthesis and degradation were evaluated in skeletal muscles. Plasma concentrations of hormones contrasted protein and fat contents in skeletal muscles. Fat weights and contents of quadriceps femoris and gastrocnemius muscles in the NP group were significantly lower compared with LP and HP groups (P < 0.05). Moreover, concentrations of factors associated with the degradation of muscle fat were significantly higher in the NP group compared with LP and HP groups (P < 0.05). During energy restriction, protein intake equal to that of a normal protein diet increased lipolysis of quadriceps femoris and gastrocnemius muscles in rats of both sexes.

Transcriptome Analysis Reveals That SREBP Modulates a Large Repertoire of Genes Involved in Key Cellular Functions in Penaeus vannamei, although the Majority of the Dysregulated Genes Are Unannotated

Sterol regulatory element-binding proteins (SREBPs) play vital roles in fatty acid metabolism and other metabolic processes in mammals. However, in penaeid shrimp, the repertoire of genes modulated by SREBP is unknown. Here, RNA interference-mediated knockdown followed by transcriptome sequencing on the Illumina Novaseq 6000 platform was used to explore the genes modulated by SREBP in Penaeus vannamei hepatopancreas. A total of 706 differentially expressed genes (DEGs) were identified, out of which 282 were upregulated and 424 downregulated. Although gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses revealed that most of the downregulated DEGs were involved in physiological processes related to immunity, metabolism, and cellular signaling pathways, many of the dysregulated genes have uncharacterized functions. While most of the dysregulated genes were annotated in metabolic processes, such as carbohydrate metabolism, lipid metabolism, signal transduction, and immune system, a large number (42.21%) are uncharacterized. Collectively, our current data revealed that SREBP modulates many genes involved in crucial physiological processes, such as energy metabolism, immune response, and cellular signaling pathways, as well as numerous genes with unannotated functions, in penaeid shrimp. These findings indicated that our knowledge of the repertoire of genes modulated by SREBP in shrimp lags behind that of mammals, probably due to limited research or because the complete genome of P. vannamei has just been sequenced.

Ablation of Tas1r1 Reduces Lipid Accumulation Through Reducing the de Novo Lipid Synthesis and Improving Lipid Catabolism in Mice

Amino acid sensing plays an important role in regulating lipid metabolism by sensing amino acid nutrient disturbance. T1R1 (umami taste receptor, type 1, member 1) is a membrane G protein-coupled receptor that senses amino acids. Tas1r1-knockout (KO) mice were used to explore the function of umami receptors in lipid metabolism. Compared with wild-type (WT) mice, Tas1r1-KO mice showed decreased fat mass (P < 0.05) and adipocyte size, lower liver triglyceride (7.835 ± 0.809 vs 12.463 ± 0.916 mg/g WT, P = 0.013) and total cholesterol levels (0.542 ± 0.109 vs 1.472 ± 0.044 mmol/g WT, P < 0.001), and reduced lipogenesis gene expressions in adipose and liver tissues. Targeted liver amino acid metabolomics showed that the amino acid content of Tas1r1-KO mice was significantly decreased, which was consistent with the branched-chain ketoacid dehydrogenase protein levels. Proteomics analysis showed that the upregulated proteins were enriched in lipid and steroid metabolism pathways, and parallel reaction monitoring results illustrated that Tas1r1 ablation promoted lipid catabolism through oxysterol 7 α-hydroxylase and insulin-like growth factor binding protein 2. In summary, Tas1r1 disruption in mice could reduce lipid accumulation by reducing de novo lipid synthesis and improving lipid catabolism.

Astrocyte-specific loss of lactoferrin influences neuronal structure and function by interfering with cholesterol synthesis

Growing evidence indicates that circulating lactoferrin (Lf) is implicated in peripheral cholesterol metabolism disorders. It has emerged that the distribution of Lf changes in astrocytes of aging brains and those exhibiting neurodegeneration; however, its physiological and/or pathological role remains unknown. Here, we demonstrate that astrocyte-specific knockout of Lf (designated cKO) led to decreased body weight and cognitive abnormalities during early life in mice. Accordingly, there was a reduction in neuronal outgrowth and synaptic structure in cKO mice. Importantly, Lf deficiency in the primary astrocytes led to decreased sterol regulatory element binding protein 2 (Srebp2) activation and cholesterol production, and cholesterol content in cKO mice and/or in astrocytes was restored by exogenous Lf or a Srebp2 agonist. Moreover, neuronal dendritic complexity and total dendritic length were decreased after culture with the culture medium of the primary astrocytes derived from cKO mice and that this decrease was reversed after cholesterol supplementation. Alternatively, these alterations were associated with an activation of AMP-activated protein kinase (AMPK) and inhibition of SREBP2 nuclear translocation. These data suggest that astrocytic Lf might directly or indirectly control in situ cholesterol synthesis, which may be implicated in neurodevelopment and several neurological diseases.

Central nervous system cholesterol metabolism in health and disease

Cholesterol is a ubiquitous and essential component of cellular membranes, as it regulates membrane structure and fluidity. Furthermore, cholesterol serves as a precursor for steroid hormones, oxysterol, and bile acids, that are essential for maintaining many of the body's metabolic processes. The biosynthesis and excretion of cholesterol is tightly regulated in order to maintain homeostasis. Although virtually all cells have the capacity to make cholesterol, the liver and brain are the two main organs producing cholesterol in mammals. Once produced, cholesterol is transported in the form of lipoprotein particles to other cell types and tissues. Upon formation of the blood-brain barrier (BBB) during embryonic development, lipoproteins cannot move between the central nervous system (CNS) and the rest of the body. As such, cholesterol biosynthesis and metabolism in the CNS operate autonomously without input from the circulation system in normal physiological conditions. Nevertheless, similar regulatory mechanisms for maintaining cholesterol homeostasis are utilized in both the CNS and peripheral systems. Here, we discuss the functions and metabolism of cholesterol in the CNS. We further focus on how different CNS cell types contribute to cholesterol metabolism, and how ApoE, the major CNS apolipoprotein, is involved in normal and pathophysiological functions. Understanding these basic mechanisms will aid our ability to elucidate how CNS cholesterol dysmetabolism contributes to neurogenerative diseases.

Metabolic Impact of MKP-2 Upregulation in Obesity Promotes Insulin Resistance and Fatty Liver Disease

The mechanisms connecting obesity with type 2 diabetes, insulin resistance, nonalcoholic fatty liver disease, and cardiovascular diseases remain incompletely understood. The function of MAPK phosphatase-2 (MKP-2), a type 1 dual-specific phosphatase (DUSP) in whole-body metabolism, and how this contributes to the development of diet-induced obesity, type 2 diabetes (T2D), and insulin resistance is largely unknown. We investigated the physiological contribution of MKP-2 in whole-body metabolism and whether MKP-2 is altered in obesity and human fatty liver disease using MKP-2 knockout mice models and human liver tissue derived from fatty liver disease patients. We demonstrate that, for the first time, MKP-2 expression was upregulated in liver tissue in humans with obesity and fatty liver disease and in insulin-responsive tissues in mice with obesity. MKP-2-deficient mice have enhanced p38 MAPK, JNK, and ERK activities in insulin-responsive tissues compared with wild-type mice. MKP-2 deficiency in mice protects against diet-induced obesity and hepatic steatosis and was accompanied by improved glucose homeostasis and insulin sensitivity. Mkp-2^−/− mice are resistant to diet-induced obesity owing to reduced food intake and associated lower respiratory exchange ratio. This was associated with enhanced circulating insulin-like growth factor-1 (IGF-1) and stromal cell-derived factor 1 (SDF-1) levels in Mkp-2^−/− mice. PTEN, a negative regulator of Akt, was downregulated in livers of Mkp-2^−/− mice, resulting in enhanced Akt activity consistent with increased insulin sensitivity. These studies identify a novel role for MKP-2 in the regulation of systemic metabolism and pathophysiology of obesity-induced insulin resistance and fatty liver disease.

Increased LDL receptor by SREBP2 or SREBP2-induced lncRNA LDLR-AS promotes triglyceride accumulation in fish

LDLR, as the uptake receptor of low-density lipoprotein, plays a crucial role in lipid metabolism. However, the detailed mechanism by which LDLR affects hepatic triglyceride (TG) accumulation has rarely been reported. Here, we found that knockdown of LDLR effectively mitigated PA-induced TG accumulation. Further analysis revealed that the expression of LDLR was controlled by SREBP2 directly and indirectly. On one hand, transcription factor SREBP2 activated the transcription of LDLR directly. On the other hand, SREBP2 indirectly regulated LDLR by increasing the transcription of lncRNA LDLR-AS in fish. Mechanism analysis found that LDLR-AS functioned as an RNA scaffold to recruit heterogeneous nuclear ribonucleoprotein R (hnRNPR) to the 5′ UTR region of LDLR mRNA, which stabilized LDLR mRNA at the post-transcription level. In conclusion, our study demonstrates that increased LDLR transcription and mRNA stability is regulated by SREBP2 directly or indirectly, and promotes hepatic TG accumulation by endocytosing LDL in fish.

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PA-mediated LDLR increases triglyceride accumulation via the uptake of LDL in fish

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SREBP2 activated by TNFα promotes LDLR transcription in fish

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LncRNA LDLR-AS increases LDLR mRNA stability by recruiting hnRNPR in fish

Investigation of the hepatic mTOR/S6K1/SREBP1 signalling pathway in rats at different ages: from neonates to adults

BACKGROUND

Dysfunctions in the lipogenic process controlled by the hepatic mTOR/S6K1/SREBP-1c signaling pathway may contribute to the pathogenesis of various chronic diseases. In the present study, we aimed to determine age-related changes in the mTOR/S6K1/SREBP1 pathway in rat liver tissues.

METHODS AND RESULTS

We performed Western Blot analysis to determine age-related changes in the mTOR/S6K1/SREBP1 pathway in Sprague Dawley male rats liver tissues of six different age groups representing neonatal, infant, weaning, puberty, young adult, adult life periods, and Oil Red O staining to evaluate age-related lipid accumulation. We observed an increase in Akt and p-Akt levels with age in compared to the 0-day-old group. Total mTOR and SREBP1 expression increased from the 0-day-old to the 28-day-old group but decreased in the following age groups. p-mTOR and p-S6K1 levels in the 0-day-old group were higher than the other groups. S6K1 expression was lowest in the 0-day-old group and showed changes among the age groups. Lipid accumulation was seen in liver sections taken from the 12-month-old group. mTOR/S6K1/SREBP1 pathway expression showed changes with age during the neonatal-adult life cycle stages in rat liver tissues.

CONCLUSION

We suggest that understanding the molecular mechanisms age-related changes of lipogenesis function is necessary to contribute to the development of therapeutic approaches.

Role of Thioredoxin-Interacting Protein in Diabetic Fatty Kidney Induced by Advanced Glycation End-Products

Advanced glycation end-products (AGEs) have been identified as the etiological factors associated with the fatty kidney. Thioredoxin-interacting protein (TXNIP) might be a mediator involved in AGE-induced fatty kidney. This study focused on investigating how TXNIP affected the AGE-mediated renal lipid deposition. In an in vivo experiment, the db/db mice injected with the lentiviral vector encoding shRNA targeting TXNIP were given the AIN-76 basal or the high-AGE diet. TXNIP-targeting siRNA-transfected human renal proximal tubular epithelial (HK-2) cells were exposed to AGE-BSA in a study in vitro. The results showed that the silencing of TXNIP reduced tubular lipid droplets and intracellular cholesterol content, as well as upregulated Insig-1 and downregulated HMGCoAR, LDLr, nSREBP-2, and SCAP in the kidneys of the db/db mice, the high-AGE-diet-fed db/db mice, and AGE-BSA-treated HK-2 cells. Furthermore, AGE-BSA enhanced SCAP-SREBP-2 complex formation while promoting their transportation to the Golgi apparatus. However, these could be inhibited by TXNIP silencing in the HK-2 cells. The above findings indicated that TXNIP knockdown mitigated the accumulation of renal tubular lipids in diabetes through the regulation of SCAP, thereby inhibiting the SCAP-SREBP-2 signaling pathway, resulting in reduced cholesterol uptake and synthesis. Therefore, TXNIP might be a potential therapeutic target to treat a diabetic fatty kidney.

TDP-43 mediates SREBF2-regulated gene expression required for oligodendrocyte myelination

Cholesterol metabolism operates autonomously within the central nervous system (CNS), where the majority of cholesterol resides in myelin. We demonstrate that TDP-43, the pathological signature protein for amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), influences cholesterol metabolism in oligodendrocytes. TDP-43 binds directly to mRNA of SREBF2, the master transcription regulator for cholesterol metabolism, and multiple mRNAs encoding proteins responsible for cholesterol biosynthesis and uptake, including HMGCR, HMGCS1, and LDLR. TDP-43 depletion leads to reduced SREBF2 and LDLR expression, and cholesterol levels in vitro and in vivo. TDP-43-mediated changes in cholesterol levels can be restored by reintroducing SREBF2 or LDLR. Additionally, cholesterol supplementation rescues demyelination caused by TDP-43 deletion. Furthermore, oligodendrocytes harboring TDP-43 pathology from FTD patients show reduced HMGCR and HMGCS1, and coaggregation of LDLR and TDP-43. Collectively, our results indicate that TDP-43 plays a role in cholesterol homeostasis in oligodendrocytes, and cholesterol dysmetabolism may be implicated in TDP-43 proteinopathies-related diseases.

Functional genomics meta-analysis to identify gene set enrichment networks in cardiac hypertrophy

In order to take advantage of the continuously increasing number of transcriptome studies, it is important to develop strategies that integrate multiple expression datasets addressing the same biological question to allow a robust analysis. Here, we propose a meta-analysis framework that integrates enriched pathways identified through the Gene Set Enrichment Analysis (GSEA) approach and calculates for each meta-pathway an empirical p-value. Validation of our approach on benchmark datasets showed comparable or even better performance than existing methods and an increase in robustness with increasing number of integrated datasets. We then applied the meta-analysis framework to 15 functional genomics datasets of physiological and pathological cardiac hypertrophy. Within these datasets we grouped expression sets measured at time points that represent the same hallmarks of heart tissue remodeling ('aggregated time points') and performed meta-analysis on the expression sets assigned to each aggregated time point. To facilitate biological interpretation, results were visualized as gene set enrichment networks. Here, our meta-analysis framework identified well-known biological mechanisms associated with pathological cardiac hypertrophy (e.g., cardiomyocyte apoptosis, cardiac contractile dysfunction, and alteration in energy metabolism). In addition, results highlighted novel, potentially cardioprotective mechanisms in physiological cardiac hypertrophy involving the down-regulation of immune cell response, which are worth further investigation.

PPDPF alleviates hepatic steatosis through inhibition of mTOR signaling

Non-alcoholic fatty liver disease (NAFLD) has become the most prevalent chronic liver disease in the world, however, no drug treatment has been approved for this disease. Thus, it is urgent to find effective therapeutic targets for clinical intervention. In this study, we find that liver-specific knockout of PPDPF (PPDPF-LKO) leads to spontaneous fatty liver formation in a mouse model at 32 weeks of age on chow diets, which is enhanced by HFD. Mechanistic study reveals that PPDPF negatively regulates mTORC1-S6K-SREBP1 signaling. PPDPF interferes with the interaction between Raptor and CUL4B-DDB1, an E3 ligase complex, which prevents ubiquitination and activation of Raptor. Accordingly, liver-specific PPDPF overexpression effectively inhibits HFD-induced mTOR signaling activation and hepatic steatosis in mice. These results suggest that PPDPF is a regulator of mTORC1 signaling in lipid metabolism, and may be a potential therapeutic candidate for NAFLD.

Non-alcoholic fatty liver disease (NAFLD) has become a prevalent chronic liver disease, however, drugs to treat this disease are still lacking. Here, the authors show that PPDPF inhibits the development of hepatic steatosis by negatively regulating mTORC1-S6K-SREBP1 signaling, which provides a potential therapeutic candidate for NAFLD treatment.

Deletion of SREBF1, a Functional Bone-Muscle Pleiotropic Gene, Alters Bone Density and Lipid Signaling in Zebrafish

Through a genome-wide analysis of bone mineral density (BMD) and muscle mass, identification of a signaling pattern on 17p11.2 recognized the presence of sterol regulatory element-binding factor 1 (SREBF1), a gene responsible for the regulation of lipid homeostasis. In conjunction with lipid-based metabolic functions, SREBF1 also codes for the protein, SREBP-1, a transcription factor known for its role in adipocyte differentiation. We conducted a quantitative correlational study. We established a zebrafish (ZF) SREBF1 knockout (KO) model and used a targeted customized lipidomics approach to analyze the extent of SREBF1 capabilities. For lipidomics profiling, we isolated the dorsal muscles of wild type (WT) and KO fishes, and we performed liquid chromatography-tandem mass spectrometry screening assays of these samples. In our analysis, we profiled 48 lipid mediators (LMs) derived from various essential polyunsaturated fatty acids to determine potential targets regulated by SREBF1, and we found that the levels of 11,12 epoxyeicosatrienoic acid (11,12-EET) were negatively associated with the number of SREBF1 alleles (P = 0.006 for a linear model). We also compared gene expression between KO and WT ZF by genome-wide RNA-sequencing. Significantly enriched pathways included fatty acid elongation, linoleic acid metabolism, arachidonic acid metabolism, adipocytokine signaling, and DNA replication. We discovered trends indicating that BMD in adult fish was significantly lower in the KO than in the WT population (P < 0.03). These studies reinforce the importance of lipidomics investigation by detailing how the KO of SREBF1 affects both BMD and lipid-signaling mediators, thus confirming the importance of SREBF1 for musculoskeletal homeostasis.

Taxifolin ameliorate high-fat-diet feeding plus acute ethanol binge-induced steatohepatitis through inhibiting inflammatory caspase-1-dependent pyroptosis

Excessive alcohol drinking and a high-fat diet (HFD) promote steatohepatitis in the comorbidity of NAFLD and AFLD. Taxifolin (TAX) is a rich dihydroxyflavone compound found in onions, milk thistle and Douglas fir. We aimed to explore the intervention mechanism of TAX on chronic steatohepatitis induced by HFD feeding plus acute ethanol binge. We established an in vivo model by HFD feeding plus a single dose of ethanol binge, and established an in vitro model by oleic acid or palmitic acid on HepG2 cells to induce lipid accumulation. TAX regulated lipid synthesis by inhibiting the expression of SREBP1 and upregulating the PPARγ level. In addition, TAX inhibited the expression of P2X7R, IL-1β, and caspase-1. Moreover, TAX reduced the expression of caspase-1 activation; thereby inhibiting the recruitment of macrophages and neutrophils. TAX also improved the inflammatory response caused by caspase-1 activation in steatotic hepatocytes. TAX exhibited an inhibitory effect on lipid accumulation and caspase-1-related pyroptosis. Collectively, TAX has therapeutic potential as an intervention of steatohepatitis induced by alcohol combined with HFD and for preventing non-alcoholic fatty liver degeneration targeting caspase-1-dependent pyroptosis.

Lipodystrophies-Disorders of the Fatty Tissue

Lipodystrophies are a heterogeneous group of physiological changes characterized by a selective loss of fatty tissue. Here, no fat cells are present, either through lack of differentiation, loss of function or premature apoptosis. As a consequence, lipids can only be stored ectopically in non-adipocytes with the major health consequences as fatty liver and insulin resistance. This is a crucial difference to being slim where the fat cells are present and store lipids if needed. A simple clinical classification of lipodystrophies is based on congenital vs. acquired and generalized vs. partial disturbance of fat distribution. Complications in patients with lipodystrophy depend on the clinical manifestations. For example, in diabetes mellitus microangiopathic complications such as nephropathy, retinopathy and neuropathy may develop. In addition, due to ectopic lipid accumulation in the liver, fatty liver hepatitis may also develop, possibly with cirrhosis. The consequences of extreme hypertriglyceridemia are typically acute pancreatitis or eruptive xanthomas. The combination of severe hyperglycemia with dyslipidemia and signs of insulin resistance can lead to premature atherosclerosis with its associated complications of coronary heart disease, peripheral vascular disease and cerebrovascular changes. Overall, lipodystrophy is rare with an estimated incidence for congenital (<1/1.000.000) and acquired (1-9/100.000) forms. Due to the rarity of the syndrome and the phenotypic range of metabolic complications, only studies with limited patient numbers can be considered. Experimental animal models are therefore useful to understand the molecular mechanisms in lipodystrophy and to identify possible therapeutic approaches.

The cellular function of SCAP in metabolic signaling

Sterol regulatory element binding protein (SREBP) cleavage activating protein (SCAP) is a key regulator of SREBP maturation. SCAP induces translocation of SREBP from the endoplasmic reticulum to the Golgi apparatus, allowing it to regulate cellular triglyceride and cholesterol levels. Previous studies have shown that suppression of SREBP activation in SCAP conditional knockout mice reduced the accumulation of intracellular triglycerides, which eventually causes the development of metabolic diseases such as atherosclerosis, diabetes, hepatic steatosis, and insulin resistance. However, despite the significance of SCAP as a regulator of SREBP, its function has not been thoroughly discussed. In this review, we have summarized the function of SCAP and its regulatory proteins. Furthermore, we discuss recent studies regarding SCAP as a possible therapeutic target for hypertriglyceridemia and hyperlipidemia.

REDD1 loss reprograms lipid metabolism to drive progression of RAS mutant tumors

In this study, Qiao et al. set out to investigate the role of REDD1 in the development of KRAS-driven tumors. Using genetically engineered mouse models, the authors show that loss of REDD1 promotes the development of oncogenic KRAS-driven pancreatic and lung cancers. Additionally, the authors use a combination of transcriptomic and metabolomic analyses to show that REDD1 deficiency induces lipid uptake, enhances fatty acid oxidation, and suppresses de novo lipid biosynthesis, in particular under hypoxia conditions, which plays an important role for the redox homeostasis of tumor cells through the regulation of NADPH levels.

Human cancers with activating RAS mutations are typically highly aggressive and treatment-refractory, yet RAS mutation itself is insufficient for tumorigenesis, due in part to profound metabolic stress induced by RAS activation. Here we show that loss of REDD1, a stress-induced metabolic regulator, is sufficient to reprogram lipid metabolism and drive progression of RAS mutant cancers. Redd1 deletion in genetically engineered mouse models (GEMMs) of KRAS-dependent pancreatic and lung adenocarcinomas converts preneoplastic lesions into invasive and metastatic carcinomas. Metabolic profiling reveals that REDD1-deficient/RAS mutant cells exhibit enhanced uptake of lysophospholipids and lipid storage, coupled to augmented fatty acid oxidation that sustains both ATP levels and ROS-detoxifying NADPH. Mechanistically, REDD1 loss triggers HIF-dependent activation of a lipid storage pathway involving PPARγ and the prometastatic factor CD36. Correspondingly, decreased REDD1 expression and a signature of REDD1 loss predict poor outcomes selectively in RAS mutant but not RAS wild-type human lung and pancreas carcinomas. Collectively, our findings reveal the REDD1-mediated stress response as a novel tumor suppressor whose loss defines a RAS mutant tumor subset characterized by reprogramming of lipid metabolism, invasive and metastatic progression, and poor prognosis. This work thus provides new mechanistic and clinically relevant insights into the phenotypic heterogeneity and metabolic rewiring that underlies these common cancers.

Leukocyte cell-derived chemotaxin 2 inhibits development of atherosclerosis in mice

Leukocyte cell-derived chemotaxin 2 (LECT2), a multifunctional hepatokine, is involved in many pathological conditions. However, its role in atherosclerosis remains undefined. In this study, we administered vehicle or LECT2 to male Apoe^-/- mice fed a Western diet for 15 weeks. Atherosclerotic lesions were visualized and quantified with Oil-red O and hematoxylin staining. The mRNA expression levels of MCP-1, MMP-1, IL-8, IL-1β, and TNF-α were analyzed by quantitative real-time polymerase chain reaction. Serum TNF-α, IL-1β, IL-8, MCP-1, and MMP-1 concentrations were measured by enzyme-linked immunosorbent assay. CD68, CD31, and α-SMA, markers of macrophages, endothelial cells, and smooth muscle cells, respectively, were detected by immunostaining. Results showed that LECT2 reduced total cholesterol and low-density lipoprotein concentrations in serum and inhibited the development of atherosclerotic lesions, accompanied by reductions in inflammatory cytokines and lower MCP-1, MMP-1, TNF-α, IL-8, and IL-1β mRNA abundance. Furthermore, LECT2 decreased CD68, but increased α-SMA in atherosclerotic lesions, suggesting an increase in smooth muscle cells and reduction in macrophages. In summary, LECT2 inhibited the development of atherosclerosis in mice, accompanied by reduced serum total cholesterol concentration and lower inflammatory responses.

Milk lipid regulation at the maternal-offspring interface

Milk lipids provide a large proportion of energy, nutrients, essential fatty acids, and signaling molecules for the newborns, the synthesis of which is a tightly controlled process. Dysregulated milk lipid production and composition may be detrimental to the growth, development, health and survival of the newborns. Many genetically modified animal models have contributed to our understanding of milk lipid regulation in the lactating mammary gland. In this review, we discuss recent advances in our knowledge of the mechanisms that control milk lipid biosynthesis and secretion during lactation, and how maternal genetic and dietary defects impact milk lipid composition and consequently offspring traits.

Inactivation of SREBP-1a Phosphorylation Prevents Fatty Liver Disease in Mice: Identification of Related Signaling Pathways by Gene Expression Profiles in Liver and Proteomes of Peroxisomes

The key lipid metabolism transcription factor sterol regulatory element-binding protein (SREBP)-1a integrates gene regulatory effects of hormones, cytokines, nutrition and metabolites as lipids, glucose, or cholesterol via phosphorylation by different mitogen activated protein kinase (MAPK) cascades. We have previously reported the impact of SREBP-1a phosphorylation on the phenotype in transgenic mouse models with liver-specific overexpression of the N-terminal transcriptional active domain of SREBP-1a (alb-SREBP-1a) or a MAPK phosphorylation site-deficient variant (alb-SREBP-1a∆P; (S63A, S117A, T426V)), respectively. In this report, we investigated the molecular basis of the systemic observations by holistic analyses of gene expression in liver and of proteome patterns in lipid-degrading organelles involved in the pathogenesis of metabolic syndrome, i.e., peroxisomes, using 2D-DIGE and mass spectrometry. The differences in hepatic gene expression and peroxisomal protein patterns were surprisingly small between the control and alb-SREBP-1a mice, although the latter develop a severe phenotype with visceral obesity and fatty liver. In contrast, phosphorylation site-deficient alb-SREBP-1a∆P mice, which are protected from fatty liver disease, showed marked differences in hepatic gene expression and peroxisomal proteome patterns. Further knowledge-based analyses revealed that disruption of SREBP-1a phosphorylation resulted in massive alteration of cellular processes, including signs for loss of targeting lipid pathways.