Structure of the human gene encoding sterol regulatory element binding protein-1 (SREBF1) and localization of SREBF1 and SREBF2 to chromosomes 17p11.2 and 22q13

A gain-of-function variant in SREBF1 causes generalized skin hyperpigmentation with congenital cataracts

BACKGROUND

Lipid metabolism has essential roles in skin barrier formation and the regulation of skin inflammation. Lipid homeostasis regulates skin melanogenesis, although the underlying mechanism remains largely unknown. Sterol regulatory element binding protein 1 (SREBP-1) is a key transcription factor essential for cellular lipid metabolism. Loss-of-function variants in SREBF1 are responsible for autosomal-dominant ichthyosis follicularis, alopecia and photophobia syndrome, emphasizing the significance of lipid homeostasis in skin keratinization.

OBJECTIVES

To identify the genetic basis of a new entity featuring diffuse skin hyperpigmentation with congenital cataracts, and to unravel the underlying mechanism for the pathogenesis of the SREBF1 variant.

METHODS

Whole-exome sequencing was performed to identify underlying genetic variants. Quantitative polymerase chain reaction, Western blot and immunofluorescence staining were used to assess the expression and the subcellular localization of the SREBF1 variant. The transcriptional activity of mutant SREBP-1 was determined by a luciferase reporter assay. A transgenic zebrafish model was constructed.

RESULTS

Two unrelated patients presented with generalized skin hyperpigmentation with skin xerosis, congenital cataracts and extracutaneous symptoms. We identified a de novo nonsense variant c.1289C>A (p.Ser430*) in SREBF1 in both patients. The variant encoded a truncated protein that showed preferential nucleus localization, in contrast to wild-type SREBP-1 which - in sterol-sufficient conditions - is mainly localized in the cytoplasm. The luciferase reporter assay revealed that the p.Ser430* mutant exhibited enhanced transcriptional activity. Cultured patient primary melanocytes showed increased melanin synthesis vs. those from healthy controls. At 35 days postfertilization, the p.Ser430* transgenic zebrafish model exhibited more black spots, along with upregulated expression of melanogenic genes.

CONCLUSIONS

We demonstrated that a gain-of-function variant of SREBF1 causes a previously undescribed disorder characterized by generalized skin hyperpigmentation and congenital cataracts. Our study reveals the involvement of SREBP-1 in melanogenesis and lens development, and paves the way for the development of novel therapeutic targets for skin dyspigmentation or cataracts.

The therapeutic effects of berberine for gastrointestinal cancers

Cancer is one of the most serious human health issues. Drug therapy is the major common way to treat cancer. There is a growing interest in using natural compounds to overcome drug resistance, adverse reactions, and target specificity of certain types of drugs that may affect several targets with fewer side effects and be beneficial against various types of cancer. In this regard, the use of herbal medicines alone or in combination with the main anticancer drugs is commonly available. Berberine (BBR), a nature-driven phytochemical component, is a well-known nutraceutical due to its wide variety of pharmacological activities, including antioxidant, anti-inflammatory, antibacterial, antifungal, antiparasitic, antidiabetic, antihypertensive, and hypolipidemic. In addition, BBR exerts anticancer activities. In present article, we summarized the information available on the therapeutic effects of BBR and its mechanisms on five types of the most prevalent gastrointestinal cancers, including esophageal, gastric, colorectal, hepatocarcinoma, and pancreatic cancers.

The Role of SCAP/SREBP as Central Regulators of Lipid Metabolism in Hepatic Steatosis

The prevalence of metabolic dysfunction-associated steatotic liver disease (MASLD) is rapidly increasing worldwide at an alarming pace, due to an increase in obesity, sedentary and unhealthy lifestyles, and unbalanced dietary habits. MASLD is a unique, multi-factorial condition with several phases of progression including steatosis, steatohepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma. Sterol element binding protein 1c (SREBP1c) is the main transcription factor involved in regulating hepatic de novo lipogenesis. This transcription factor is synthesized as an inactive precursor, and its proteolytic maturation is initiated in the membrane of the endoplasmic reticulum upon stimulation by insulin. SREBP cleavage activating protein (SCAP) is required as a chaperon protein to escort SREBP from the endoplasmic reticulum and to facilitate the proteolytic release of the N-terminal domain of SREBP into the Golgi. SCAP inhibition prevents activation of SREBP and inhibits the expression of genes involved in triglyceride and fatty acid synthesis, resulting in the inhibition of de novo lipogenesis. In line, previous studies have shown that SCAP inhibition can resolve hepatic steatosis in animal models and intensive research is going on to understand the effects of SCAP in the pathogenesis of human disease. This review focuses on the versatile roles of SCAP/SREBP regulation in de novo lipogenesis and the structure and molecular features of SCAP/SREBP in the progression of hepatic steatosis. In addition, recent studies that attempt to target the SCAP/SREBP axis as a therapeutic option to interfere with MASLD are discussed.

SIRT1/SREBPs-mediated regulation of lipid metabolism

Sirtuins, also called silent information regulator 2, are enzymes that rely on nicotinamide adenine dinucleotide (NAD+) to function as histone deacetylases. Further investigation is warranted to explore the advantageous impacts of Sirtuin 1 (SIRT1), a constituent of the sirtuin group, on lipid metabolism, in addition to its well-researched involvement in extending lifespan. The regulation of gene expression has been extensively linked to SIRT1. Sterol regulatory element-binding protein (SREBP) is a substrate of SIRT1 that has attracted significant interest due to its role in multiple cellular processes including cell cycle regulation, DNA damage repair, and metabolic functions. Hence, the objective of this analysis was to investigate and elucidate the correlation between SIRT1 and SREBPs, as well as assess the contribution of SIRT1/SREBPs in mitigating lipid metabolism dysfunction. The objective of this research was to investigate whether SIRT1 and SREBPs could be utilized as viable targets for therapeutic intervention in managing complications associated with diabetes.

Circadian clock and lipid metabolism disorders: a potential therapeutic strategy for cancer

Recent research has emphasized the interaction between the circadian clock and lipid metabolism, particularly in relation to tumors. This review aims to explore how the circadian clock regulates lipid metabolism and its impact on carcinogenesis. Specifically, targeting key enzymes involved in fatty acid synthesis (SREBP, ACLY, ACC, FASN, and SCD) has been identified as a potential strategy for cancer therapy. By disrupting these enzymes, it may be possible to inhibit tumor growth by interfering with lipid metabolism. Transcription factors, like SREBP play a significant role in regulating fatty acid synthesis which is influenced by circadian clock genes such as BMAL1, REV-ERB and DEC. This suggests a strong connection between fatty acid synthesis and the circadian clock. Therefore, successful combination therapy should target fatty acid synthesis in addition to considering the timing and duration of drug use. Ultimately, personalized chronotherapy can enhance drug efficacy in cancer treatment and achieve treatment goals.

Evolutionary analysis of buffalo sterol regulatory element-binding factor (SREBF) family genes and their affection on milk traits

The sterol regulatory element-binding factor (SREBF) genes are a vital group of proteins binding to the sterol regulatory element 1 (SRE-1) regulating the synthesis of fatty acid. Two potential candidate genes (SREBF1 and SREBF2) have been identified as affecting milk traits. This study aims to identify the SREBF family of genes and find candidate markers or SREBF genes influencing lactation production in buffalo. A genome-wide study was performed and identified seven SREBF genes randomly distributed on 7 chromosomes and 24 protein isoforms in buffalos. The SREBF family of genes were also characterized in cattle, goat, sheep and horse, and using these all-protein sequences, a phylogenetic tree was built. The SREBF family genes were homologous between each other in the five livestock. Eight single nucleotide polymorphisms (SNPs) within or near the SREBF genes in the buffalo genome were identified and at least one milk production trait was associated with three of the SNP. The expression of SREBF genes at different lactation stages in buffalo and cattle from published data were compared and the SREBF genes retained a high expression throughout lactation with the trend being the same for buffalo and cattle. These results provide valuable information for clarifying the evolutionary relationship of the SREBF family genes and determining the role of SREBF genes in the regulation of milk production in buffalo.

Adverse outcome pathway for pregnane X receptor-induced hypercholesterolemia

Pharmaceuticals and environmental contaminants contribute to hypercholesterolemia. Several chemicals known to cause hypercholesterolemia, activate pregnane X receptor (PXR). PXR is a nuclear receptor, classically identified as a sensor of chemical environment and regulator of detoxification processes. Later, PXR activation has been shown to disrupt metabolic functions such as lipid metabolism and recent findings have shown PXR activation to promote hypercholesterolemia through multiple mechanisms. Hypercholesterolemia is a major causative risk factor for atherosclerosis and greatly promotes global health burden. Metabolic disruption by PXR activating chemicals leading to hypercholesterolemia represents a novel toxicity pathway of concern and requires further attention. Therefore, we constructed an adverse outcome pathway (AOP) by collecting the available knowledge considering the molecular mechanisms for PXR-mediated hypercholesterolemia. AOPs are tools of modern toxicology for systematizing mechanistic knowledge to assist health risk assessment of chemicals. AOPs are formalized and structured linear concepts describing a link between molecular initiating event (MIE) and adverse outcome (AO). MIE and AO are connected via key events (KE) through key event relationships (KER). We present a plausible route of how PXR activation (MIE) leads to hypercholesterolemia (AO) through direct regulation of cholesterol synthesis and via activation of sterol regulatory element binding protein 2-pathway.

Differentially Expressed mRNA in Streptozotocin-Induced Diabetic Bladder Using RNA Sequencing Analysis

PURPOSE

To detect elements governing the pathogenesis of diabetic cystopathy (DC), mRNA sequencing was carried out for bladder tissues from normal rats and those with induced diabetes mellitus (DM). This research therefore offers possible underlying molecular pathways for the advancement of DC in relation to differential mRNA expression, together with visceral functional and architectural alterations noted in individuals with this condition.

METHODS

An intraperitoneal injection of streptozotocin (STZ) was utilized to provoke DM in male Sprague-Dawley rats. Dysregulation and significant variations between normal rats and those with induced DM were then identified by a fold change of ≥ 1.5 with a false discovery rate P < 0.05. Hierarchical clustering/heat map and Gene Ontology/DAVID reference sources were generated. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis and protein-protein interaction analysis were then performed.

RESULTS

The diabetic rodent group exhibited a greater residual urine volume (4.0 ± 0.4 mL) than their control counterparts (0.7 ± 0.2 mL, P < 0.01) at 12 weeks after diagnosis of diabetes. Expression analysis revealed 16 upregulated and 4 downregulated genes in STZDM bladder samples. A notable increase in expression was seen in PTHLH, TNFAIP6, PRC1, MAPK10, LOC686120, CASQ2, ACTG2, PDLIM3, FCHSD1, DBN1, NKD2, PDLIM7, ATF4, RBPMS2, ITGB1 and HSPB8. A notable decrease in expression was seen in SREBLF1, PBGFR1, PBLD1 and CELF1. Major genetic themes associated with mRNA upregulation and downregulation ware identified via Gene Ontology analysis and KEGG pathways. Protein to protein interaction analysis detected PDLIM3, PDLIM7, ITGB1, ACTG2 as core high frequency nodes within the network.

CONCLUSION

Changes in mRNA expression together with biological process and pathways that contribute to the etiologies underlying visceral impairment of the bladder in DM are evident. Our strategy is promising for recognizing mRNAs exclusive to the bladder in DM that might offer useful targets for diagnosis and treatment.

Genetic and metabolic aspects of non-alcoholic fatty liver disease (NAFLD) pathogenicity

Background

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease showing a rising prevalence globally. Genetic predisposition plays a key role in the development and progression of the disease pathogenicity.

Main body

This paper summarizes genetic associations based on their influence on several metabolic aspects such as lipid metabolism, glucose metabolism, hepatic iron accumulation and cholesterol metabolism toward the NAFLD pathogenicity. Furthermore, we present variations in some epigenetic characters and the microRNA profile with regard to NAFLD.

Conclusion

As reported in many studies, the PNPLA3 rs738409 variant seems to be significantly associated with NAFLD susceptibility. Other gene variants like TM6SF2 rs58542926, MBOAT7 rs641738 and GCKR variants also appear to be more prevalent among NAFLD patients. We believe these genetic variants may provide insights into new trends in developing noninvasive biomarkers and identify their suitability in clinical practice in the future.

Graphical abstract

From worms to humans: Understanding intestinal lipid metabolism via model organisms

The intestine is responsible for efficient absorption and packaging of dietary lipids before they enter the circulatory system. This review provides a comprehensive overview of how intestinal enterocytes from diverse model organisms absorb dietary lipid and subsequently secrete the largest class of lipoproteins (chylomicrons) to meet the unique needs of each animal. We discuss the putative relationship between diet and metabolic disease progression, specifically Type 2 Diabetes Mellitus. Understanding the molecular response of intestinal cells to dietary lipid has the potential to undercover novel therapies to combat metabolic syndrome.

Targeting SREBP-1-Mediated Lipogenesis as Potential Strategies for Cancer

Sterol regulatory element binding protein-1 (SREBP-1), a transcription factor with a basic helix–loop–helix leucine zipper, has two isoforms, SREBP-1a and SREBP-1c, derived from the same gene for regulating the genes of lipogenesis, including acetyl-CoA carboxylase, fatty acid synthase, and stearoyl-CoA desaturase. Importantly, SREBP-1 participates in metabolic reprogramming of various cancers and has been a biomarker for the prognosis or drug efficacy for the patients with cancer. In this review, we first introduced the structure, activation, and key upstream signaling pathway of SREBP-1. Then, the potential targets and molecular mechanisms of SREBP-1-regulated lipogenesis in various types of cancer, such as colorectal, prostate, breast, and hepatocellular cancer, were summarized. We also discussed potential therapies targeting the SREBP-1-regulated pathway by small molecules, natural products, or the extracts of herbs against tumor progression. This review could provide new insights in understanding advanced findings about SREBP-1-mediated lipogenesis in cancer and its potential as a target for cancer therapeutics.

Effect of dietary soybean oil inclusion on liver-related transcription factors in a pig model for metabolic diseases

Dietary fatty acids (FA) are components of the lipids, which contribute to membrane structure, energy input, and biological functions related to cellular signaling and transcriptome regulation. However, the consumers still associate dietary FA with fat deposition and increased occurrence of metabolic diseases such as obesity and atherosclerosis. Previous studies already demonstrated that some fatty acids are linked with inflammatory response, preventing metabolic diseases. To better understand the role of dietary FA on metabolic diseases, for the first time, a study to identify key transcription factors (TF) involved in lipid metabolism and inflammatory response by transcriptome analysis from liver samples of animal models was performed. The key TF were identified by functional enrichment analysis from the list of differentially expressed genes identified in liver samples between 35 pigs fed with 1.5% or 3.0% soybean oil. The functional enrichment analysis detected TF linked to lipid homeostasis and inflammatory response, such as RXRA, EGFR, and SREBP2 precursor. These findings demonstrated that key TF related to lipid metabolism could be modulated by dietary inclusion of soybean oil. It could contribute to nutrigenomics research field that aims to elucidate dietary interventions in animal and human health, as well as to drive food technology and science.

Fatty Acid Metabolism and T Cells in Multiple Sclerosis

Cellular metabolic remodeling is intrinsically linked to the development, activation, differentiation, function, and survival of T cells. T cells transition from a catabolic, naïve state to an anabolic effector state upon T cell activation. Subsequently, specialization of T cells into T helper (Th) subsets, including regulatory T cells (Treg), requires fine-tuning of metabolic programs that better support and optimize T cell functions for that particular environment. Increasingly, studies have shown that changes in nutrient availability at both the cellular and organismal level during disease states can alter T cell function, highlighting the importance of better characterizing metabolic-immune axes in both physiological and disease settings. In support of these data, a growing body of evidence is emerging that shows specific lipid species are capable of altering the inflammatory functional phenotypes of T cells. In this review we summarize the metabolic programs shown to support naïve and effector T cells, and those driving Th subsets. We then discuss changes to lipid profiles in patients with multiple sclerosis, and focus on how the presence of specific lipid species can alter cellular metabolism and function of T cells.

Natural Small Molecules in Breast Cancer Treatment: Understandings from a Therapeutic Viewpoint

Breast cancer (BrCa) is the most common malignancy in women and the second most significant cause of death from cancer. BrCa is one of the most challenging malignancies to treat, and it accounts for a large percentage of cancer-related deaths. The number of cases requiring more effective BrCa therapy has increased dramatically. Scientists are looking for more productive agents, such as organic combinations, for BrCa prevention and treatment because most chemotherapeutic agents are linked to cancer metastasis, the resistance of the drugs, and side effects. Natural compounds produced by living organisms promote apoptosis and inhibit metastasis, slowing the spread of cancer. As a result, these compounds may delay the spread of BrCa, enhancing survival rates and reducing the number of deaths caused by BrCa. Several natural compounds inhibit BrCa production while lowering cancer cell proliferation and triggering cell death. Natural compounds, in addition to therapeutic approaches, are efficient and potential agents for treating BrCa. This review highlights the natural compounds demonstrated in various studies to have anticancer properties in BrCa cells. Future research into biological anti-BrCa agents may pave the way for a new era in BrCa treatment, with natural anti-BrCa drugs playing a key role in improving BrCa patient survival rates.

SETD8 stabilized by USP17 epigenetically activates SREBP1 pathway to drive lipogenesis and oncogenesis of ccRCC

Recently, epigenetic modifications, including DNA methylation, histone modification and noncoding RNA (ncRNA)-associated gene silencing, have received increasing attention from the scientific community. Many studies have demonstrated that epigenetic regulation can render dynamic alterations in the transcriptional potential of a cell, which then affects the cell's biological function. The initiation and development of clear cell renal cell carcinoma (ccRCC), the most common subtype of renal cell cancer (RCC), is also closely related to genomic alterations by epigenetic modification. For ccRCC, lipid accumulation is one of the most typical characteristics. In other words, dysregulation of lipid uptake and synthesis occurs in ccRCC, which inversely promotes cancer proliferation and progression. However, the link among epigenetic alterations, lipid biosynthesis and renal cancer progression remains unclear. SETD8 is a histone methyltransferase and plays pivotal roles in cell cycle regulation and oncogenesis of various cancers, but its role in RCC is not well understood. In this study, we discovered that SETD8 was significantly overexpressed in RCC tumors, which was positively related to lipid storage and correlated with advanced tumor grade and stage and poor patient prognosis. Depletion of SETD8 by siRNAs or inhibitor UNC0379 diminished fatty acid (FA) de novo synthesis, cell proliferation and metastasis in ccRCC cells. Mechanistically, SETD8, which was posttranslationally stabilized by USP17, could transcriptionally modulate sterol regulatory element-binding protein 1 (SREBP1), a key transcription factor in fatty acid biosynthesis and lipogenesis, by monomethylating the 20th lysine of the H4 histone, elevating lipid biosynthesis and accumulation in RCC and further promoting cancer progression and metastasis. Taken together, the USP17/SETD8/SREBP1 signaling pathway plays a pivotal role in promoting RCC progression. SETD8 might be a novel biomarker and potential therapeutic target for treating RCC.

Elevated Plasma Free Fatty Acid Susceptible to Early Cognitive Impairment in Type 2 Diabetes Mellitus

BACKGROUND

Elevated free fatty acid (FFA) induces lipotoxicity, attributed to diabetes and cognitive decline. Sterol regulatory element-binding protein-1c (SREBP-1c) regulates lipid metabolism.

OBJECTIVE

We investigated the roles of FFA in mild cognitive impairment (MCI) of type 2 diabetes mellitus (T2DM) patients and determine its association with rs11868035 polymorphism.

METHODS

We recruited 191 Chinese T2DM patients into two groups through Montreal Cognitive Assessment. Demographic and clinical data were collected, multiple domain cognitive functions were tested, plasma FFA levels were measured through ELISA, and SREBP-1c rs11868035 genotype was detected using the Seqnome method.

RESULTS

In comparison with the healthy-cognition group (n = 128), the MCI group (n = 63) displayed lower glucose control (p = 0.012) and higher plasma FFA level (p = 0.021), which were independent risk factors of MCI in T2DM patients in multivariate regression analysis (OR = 1.270, p = 0.003; OR = 1.005, p = 0.036). Additionally, the plasma FFA levels of MCI patients were positively correlated with Stroop color word test-C time scores (r = 0.303, p = 0.021) and negatively related to apolipoprotein A1 levels (r = -0.311, p = 0.017), which are associated positively with verbal fluency test scores (r = 0.281, p = 0.033). Both scores reflected attention ability and executive function. Moreover, the G allele carriers of rs11868035 showed higher digit span test scores than non-carriers in T2DM patients (p = 0.019) but without correlation with plasma FFA levels.

CONCLUSION

In T2DM, elevated plasma level of FFA, when combined with lower apolipoprotein A1 level portends abnormal cholesterol transport, were susceptible to early cognitive impairment, especially for attention and execution deficits. The G allele of SREBP-1c rs11868035 may be a protective factor for memory.

SREBP-1c Deficiency Affects Hippocampal Micromorphometry and Hippocampus-Dependent Memory Ability in Mice

Changes in structural and functional neuroplasticity have been implicated in various neurological disorders. Sterol regulatory element-binding protein (SREBP)-1c is a critical regulatory molecule of lipid homeostasis in the brain. Recently, our findings have shown the potential involvement of SREBP-1c deficiency in the alteration of novel modulatory molecules in the hippocampus and occurrence of schizophrenia-like behaviors in mice. However, the possible underlying mechanisms, related to neuronal plasticity in the hippocampus, are yet to be elucidated. In this study, we investigated the hippocampus-dependent memory function and neuronal architecture of hippocampal neurons in SREBP-1c knockout (KO) mice. During the passive avoidance test, SREBP-1c KO mice showed memory impairment. Based on Golgi staining, the dendritic complexity, length, and branch points were significantly decreased in the apical cornu ammonis (CA) 1, CA3, and dentate gyrus (DG) subregions of the hippocampi of SREBP-1c KO mice, compared with those of wild-type (WT) mice. Additionally, significant decreases in the dendritic diameters were detected in the CA3 and DG subregions, and spine density was also significantly decreased in the apical CA3 subregion of the hippocampi of KO mice, compared with that of WT mice. Alterations in the proportions of stubby and thin-shaped dendritic spines were observed in the apical subcompartments of CA1 and CA3 in the hippocampi of KO mice. Furthermore, the corresponding differential decreases in the levels of SREBP-1 expression in the hippocampal subregions (particularly, a significant decrease in the level in the CA3) were detected by immunofluorescence. This study suggests that the contributions of SREBP-1c to the structural plasticity of the mouse hippocampus may have underlain the behavioral alterations. These findings offer insights into the critical role of SREBP-1c in hippocampal functioning in mice.

Regulation of Osteoclast Differentiation and Activity by Lipid Metabolism

Bone is a dynamic tissue and is constantly being remodeled by bone cells. Metabolic reprogramming plays a critical role in the activation of these bone cells and skeletal metabolism, which fulfills the energy demand for bone remodeling. Among various metabolic pathways, the importance of lipid metabolism in bone cells has long been appreciated. More recent studies also establish the link between bone loss and lipid-altering conditions—such as atherosclerotic vascular disease, hyperlipidemia, and obesity—and uncover the detrimental effect of fat accumulation on skeletal homeostasis and increased risk of fracture. Targeting lipid metabolism with statin, a lipid-lowering drug, has been shown to improve bone density and quality in metabolic bone diseases. However, the molecular mechanisms of lipid-mediated regulation in osteoclasts are not completely understood. Thus, a better understanding of lipid metabolism in osteoclasts can be used to harness bone cell activity to treat pathological bone disorders. This review summarizes the recent developments of the contribution of lipid metabolism to the function and phenotype of osteoclasts.

Transcriptional regulation mechanism of sterol regulatory element binding proteins on Δ6 fatty acyl desaturase in razor clam Sinonovacula constricta

The razor clam, Sinonovacula constricta, contains high levels of long-chain PUFA (LC-PUFA), which are critical for human health. In addition, S. constricta is the first marine mollusc demonstrated to possess Δ6 fatty acyl desaturase (Fad) and complete LC-PUFA biosynthetic ability, providing a good representative to investigate the molecular mechanism of sterol regulatory element binding proteins (SREBP) in regulating Δ6 Fad for LC-PUFA biosynthesis in marine molluscs. Herein, S. constricta SREBP and Δ6 Fad promoter were cloned and characterised. Subsequently, dual luciferase and electrophoretic mobility shift assays were conducted to explore the SREBP binding elements in the core regulatory region of S. constricta Δ6 Fad promoter. Results showed that S. constricta SREBP had a very conservative basic helix-loop-helix-leucine zipper motif, while S. constricta Δ6 Fad promoter exhibited very poor identity with teleost Fads2 promoters, indicating their differentiation during evolution. A 454 bp region harbouring a core sequence in S. constricta Δ6 Fad promoter was predicted to be essential for the transcriptional activation by SREBP. This was the first report on the regulatory mechanism of LC-PUFA biosynthesis in marine molluscs, which would facilitate optimising the LC-PUFA biosynthetic pathway of bivalves in further studies.

Transcriptome Profiling Reveals Novel Candidate Genes Related to Hippocampal Dysfunction in SREBP-1c Knockout Mice

Lipid homeostasis is an important component of brain function, and its disturbance causes several neurological disorders, such as Huntington's, Alzheimer's, and Parkinson's diseases as well as mood disorders. Sterol regulatory element-binding protein-1c (SREBP-1c) is a key modulatory molecule involved in lipid homeostasis in the central nervous system. However, little is known about the biological effects of SREBP-1c in the brain. Our previous study uncovered that mice deficient in SREBP-1c exhibit schizophrenia-like behaviors. To investigate whether there are novel molecular mechanisms involved in the neurological aberrations caused by SREBP-1c deficiency, we analyzed the transcriptomes of the hippocampus of SREBP-1c knockout (KO) mice and wild-type mice. We found seven differentially expressed genes (three up-regulated and four down-regulated genes) in the hippocampus of SREBP-1c KO mice. For further verification, we selected the three most significantly changed genes: glucagon-like peptide 2 receptors (GLP2R) involved in hippocampal neurogenesis and neuroplasticity as well as in cognitive impairments; necdin (NDN) which is related to neuronal death and neurodevelopmental disorders; and Erb-B2 receptor tyrosine kinase 4 (ERBB4) which is a receptor for schizophrenia-linked protein, neuregulin-1. The protein levels of GLP2R and NDN were considerably decreased, but the level of ERBB4 was significantly increased in the hippocampus of SREBP-1c KO mice. However, further confirmation is warranted to establish the translatability of these findings from this rodent model into human patients. We suggest that these data provide novel molecular evidence for the modulatory role of SREBP-1c in the mouse hippocampus.

Fatty Acids and Effects on In Vitro and In Vivo Models of Liver Steatosis

BACKGROUND

Fatty liver, or steatosis, is a condition of excess accumulation of lipids, mainly under form of triglycerides (TG), in the liver, and it is the hallmark of non-alcoholic fatty liver disease (NAFLD). NAFLD is the most common liver disorder world-wide and it has frequently been associated with obesity, hyperlipidemia and insulin resistance. Free fatty acids (FA) are the major mediators of hepatic steatosis; patients with NAFLD have elevated levels of circulating FA that correlate with disease severity.

METHODS

Steatosis is a reversible condition that can be resolved with changed behaviors, or that can progress towards more severe liver damages such as steatohepatitis (NASH), fibrosis and cirrhosis. In NAFLD, FA of exogenous or endogenous origin accumulate in the hepatocytes and trigger liver damages. Excess TG are stored in cytosolic lipid droplets (LDs) that are dynamic organelles acting as hubs for lipid metabolism.

RESULTS

In the first part of this review, we briefly reassumed the main classes of FA and their chemical classification as a function of the presence and number of double bonds, their metabolic pathways and effects on human health. Then, we summarized the main genetic and diet-induced animal models of NAFLD, as well as the cellular models of NAFLD.

CONCLUSIONS

In recent years, both the diet-induced animal models of NAFLD as well as the cellular models of NAFLD have found ever more application to investigate the mechanisms involved in NAFLD, and we referred to their advantages and disadvantages.

Targeting SREBP1 chemosensitizes colorectal cancer cells to gemcitabine by caspase-7 upregulation

Biomarkers for predicting chemotherapy response are important for treatment of colorectal cancer (CRC) patients.SREBP1is involved in cancer cell chemoresistance, but the biological consequences of this activity in CRC are poorly understood. We set up biochemical and cell biology analyzes to analyze SREBP1 expression and chemoresistance. We found that SREBP1 was overexpressed in chemoresistant CRC samples, and that SREBP1 overexpression was correlated with poorer patient survival. Targeting SREBP1 increased chemosensitivity to gemcitabine (Gem) in CRC cells. Additionally, SREBP1 overexpression increased chemoresistance to Gem in CRC cells. SREBP1 overexpression downregulated caspase-7 and decreased CRC cell sensitivity to Gem. Low SREBP1 expression was correlated with high caspase-7 expression in CRC patient samples. Low caspase-7 expression was correlated with poor patient survival. Our findings indicated that upregulation of caspase-7 caused by downregulation of SREBP1 may be a novel prognostic biomarker, and may represent a new therapeutic target in CRC.

Liver transcriptome profiling of beef steers with divergent growth rate, feed intake, or metabolic body weight phenotypes1

Average daily gain (ADG) and daily dry matter intake (DMI) are key determinants of beef industry profitability. These traits together with metabolic body weight (MWT) are combined as component traits to calculate residual feed intake (RFI), a common measure of feed efficiency in beef cattle. Recently, there have been significant efforts towards molecular genetic characterization of RFI through transcriptomic studies in different breeds and tissues. However, molecular mechanisms of RFI component traits still remain predominately unexplored. Therefore, in the current study, we investigated the hepatic transcriptomic profiles and their associations with ADG, DMI, and MWT in Angus, Charolais, and Kinsella Composite (KC) populations through global RNAseq analyses. In each population and for each trait, 12 steers with extreme phenotypes (n = 6 low and n = 6 high) were analyzed for differential gene expression. These animals were from 20 beef steers of each Angus, Charolais, and KC breed population that were initially selected for a transcriptome study of RFI. At a false discovery rate <0.05 and fold change >1.5, we identified 123, 102, and 78 differentially expressed (DE) genes between high- and low-ADG animals of Angus, Charolais, and KC populations, respectively. For DMI, 108, 180, and 156 DE genes were identified between high- and low-DMI from Angus, Charolais, and KC populations, respectively, while for MWT, 80, 82, and 84 genes were differentially expressed between high- and low-MWT animals in Angus, Charolais, and KC populations, respectively. The identified DE genes were largely breed specific (81.7% for ADG, 82.7% for DMI, and 83% for MWT), but were largely involved in the same biological functions across the breeds. Among the most enriched biological functions included metabolism of major nutrients (lipids, carbohydrates, amino acids, vitamins, and minerals), small molecule biochemistry, cellular movement, cell morphology, and cell-to-cell signaling and interaction. Notably, we identified multiple DE genes that are involved in cholesterol biosynthesis, and immune response pathways for the 3 studied traits. Thus, our findings present potential molecular genetic mechanisms and candidate genes that influence feed intake, growth, and MWT of beef cattle.

Industrial Trans Fatty Acids Stimulate SREBP2-Mediated Cholesterogenesis and Promote Non-Alcoholic Fatty Liver Disease

SCOPE

The mechanisms underlying the deleterious effects of trans fatty acids on plasma cholesterol and non-alcoholic fatty liver disease (NAFLD) are unclear. Here, the aim is to investigate the molecular mechanisms of action of industrial trans fatty acids.

METHODS AND RESULTS

Hepa1-6 hepatoma cells were incubated with elaidate, oleate, or palmitate. C57Bl/6 mice were fed diets rich in trans-unsaturated, cis-unsaturated, or saturated fatty acids. Transcriptomics analysis of Hepa1-6 cells shows that elaidate but not oleate or palmitate induces expression of genes involved in cholesterol biosynthesis. Induction of cholesterogenesis by elaidate is mediated by increased sterol regulatory element-binding protein 2 (SREBP2) activity and is dependent on SREBP cleavage-activating protein (SCAP), yet independent of liver-X receptor and ubiquitin regulatory X domain-containing protein 8. Elaidate decreases intracellular free cholesterol levels and represses the anticholesterogenic effect of exogenous cholesterol. In mice, the trans-unsaturated diet increases the ratio of liver to gonadal fat mass, steatosis, hepatic cholesterol levels, alanine aminotransferase activity, and fibrosis markers, suggesting enhanced NAFLD, compared to the cis-unsaturated and saturated diets.

CONCLUSION

Elaidate induces cholesterogenesis in vitro by activating the SCAP-SREBP2 axis, likely by lowering intracellular free cholesterol and attenuating cholesterol-dependent repression of SCAP. This pathway potentially underlies the increase in liver cholesterol and NAFLD by industrial trans fatty acids.

Isolation, characterization, and SREBP1 functional analysis of mammary epithelial cell in buffalo

Compared to cow milk, buffalo milk contains more protein, fat, and vitamin. Buffalo milk is an ideal food in human life. Sterol regulatory element-binding protein 1 (SREBP1), an important transcription factor, regulates the expression and activity of enzyme and protein involved in milk fat synthesis to influence on the synthesis and secretion of triglyceride in mammary epithelial cells. In the present study, we successfully isolated buffalo mammary epithelial cell by using enzymatic digestion, and then described the growth characteristics and expression characteristics of mammary epithelial cells. Moreover, we cloned the SREBP1 gene from total RNA isolated from milk fat globule and analyzed the function of the SREBP1 gene. After infected with shRNA-SREBP1 lentiviral particle and treated with fatty acid, the expression trend of ACACA, FABP3, FAS, SCD, ERK1, ERK2, PPARy, and Insigl genes was consistent with the expression trend of SREBP1 gene. These results suggested that SREBP1 gene is a central transcription factor in regulating milk fat synthesis and SREBP1 gene may act on ERK1/ERK2 signaling pathway to regulate the expression of PPARy gene. The current study will provide a theoretical basis for further reveal the molecular mechanism of milk fat synthesis in buffalo mammary epithelial cells. PRACTICAL APPLICATIONS: This study aim to separate and analysis characterization of mammary epithelial cell in buffalo. Compared to cow milk, buffalo milk contains more protein, fat, and vitamin. Buffalo milk is an ideal food in human life. This study will provide a theoretical basis for further research on the molecular mechanism of milk fat synthesis in buffalo mammary epithelial cells.

SREBP1 promotes the invasion of colorectal cancer accompanied upregulation of MMP7 expression and NF-κB pathway activation

BACKGROUND

Sterol-regulatory element binding protein 1 (SREBP1), an intracellular cholesterol sensor located in the endoplasmic reticulum, regulates the intracellular cholesterol by the Insig-Srebp-Scap pathway. Over-expression of SREBP1 can cause dyslipidemia. SREBP1 can regulate the metabolic pathway, and then promote the proliferation of tumor cells. However, there is no relevant research of metastasis and invasion in the field of colorectal cancer (CRC).

METHODS

Expression of SREBP1 was manipulated in CRC cell lines with low and high level SREBP1 expression by transfectiong with plasmids containing the SREBP1 gene, or by shRNA. The effect of SREBP1 on cell migration was assayed. The expression of SREBP1, p65 and MMP7 were detected by western blot. Human umbilical vein endothelial cell was used for detection of angiogenesis by adding the culture supernatant from HT29 and SW620. The level of reactive oxygen species (ROS) was detected by Dihydroethidium (DHE) staining. NF-κB inhibitor SN50 was used to test the relationship of SREBP1, NF-κB pathway and MMP7.

RESULTS

We found that the expression of SREBP1 in colon adenocarcinoma was significantly higher than that in noncancerous tissues, especially in the invasive tumor front including tumor budding. In vitro, SREBP1 over-expressed in colon cancer cell lines HT29 promoted angiogenesis in endothelial cells, increased ROS levels, phosphorylation of NF-κB-p65 and increases MMP7 expression. The effect of SREBP1 on expression of MMP7 was lost following treatment with the NF-κB inhibitor SN50.

CONCLUSION

Our results suggest that SREBP1 can promote the invasion and metastasis of CRC cells by means of promoting the expression of MMP7 related to phosphorylation of p65.

Deficiency of sterol regulatory element-binding protein-1c induces schizophrenia-like behavior in mice

Schizophrenia is a hereditary disease that approximately 1% of the worldwide population develops. Many studies have investigated possible underlying genes related to schizophrenia. Recently, clinical studies suggested sterol regulatory element-binding protein (SREBP) as a susceptibility gene in patients with schizophrenia. SREBP controls cellular lipid homeostasis by three isoforms: SREBP-1a, SREBP-1c and SREBP-2. This study used SREBP-1c knockout (KO) mice to examine whether a deficiency in SREBP-1c would affect their emotional and psychiatric behaviors. Altered mRNA expression in genes downstream from SREBP-1c was confirmed in the brains of SREBP-1c KO mice. Schizophrenia-like behavior, including hyperactivity during the dark phase, depressive-like behavior, aggressive behavior and deficits in social interaction and prepulse inhibition, was observed in SREBP-1c KO mice. Furthermore, increased volume of the lateral ventricle was detected in SREBP-1c KO mice. The mRNA levels of several γ-aminobutyric acid (GABA)-receptor subtypes and/or glutamic acid decarboxylase 65/67 decreased in the hippocampus and medial prefrontal cortex of SREBP-1c KO mice. Thus, SREBP-1c deficiency may contribute to enlargement of the lateral ventricle and development of schizophrenia-like behaviors and be associated with altered GABAergic transmission.

The contribution of cholesterol and epigenetic changes to the pathophysiology of breast cancer

Breast cancer​ is one of the most commonly diagnosed cancers in women. Accumulating evidence suggests that cholesterol plays an important role in the development of breast cancer. Even though the mechanistic link between these two factors is not well understood, one possibility is that dysregulated cholesterol metabolism may affect lipid raft and membrane fluidity and can promote tumor development. Current studies have shown oxysterol 27-hydroxycholesterol (27-HC) as a critical regulator of cholesterol and breast cancer pathogenesis. This is supported by the significantly higher expression of CYP27A1 (cytochrome P450, family 27, subfamily A, polypeptide 1) in breast cancers. This enzyme is responsible for 27-HC synthesis from cholesterol. It has been shown that 27-HC can not only increase the proliferation of estrogen receptor (ER)-positive breast cancer cells but also stimulate tumor growth and metastasis in several breast cancer models. This phenomenon is surprising since 27-HC and other oxysterols generally reduce intracellular cholesterol levels by activating the liver X receptors (LXRs). Resolving this paradox will elucidate molecular pathways by which cholesterol, ER, and LXR are connected to breast cancer. These findings will also provide the rationale for evaluating pharmaceutical approaches that manipulate cholesterol or 27-HC synthesis in order to mitigate the impact of cholesterol on breast cancer pathophysiology. In addition to cholesterol, epigenetic changes including non-coding RNAs, and microRNAs, DNA methylation, and histone modifications, have all been shown to control tumorigenesis. The purpose of this review is to discuss the link between altered cholesterol metabolism and epigenetic modification during breast cancer progression.

Regulation and Metabolic Significance of De Novo Lipogenesis in Adipose Tissues

De novo lipogenesis (DNL) is a complex and highly regulated process in which carbohydrates from circulation are converted into fatty acids that are then used for synthesizing either triglycerides or other lipid molecules. Dysregulation of DNL contributes to human diseases such as obesity, type 2 diabetes, and cardiovascular diseases. Thus, the lipogenic pathway may provide a new therapeutic opportunity for combating various pathological conditions that are associated with dysregulated lipid metabolism. Hepatic DNL has been well documented, but lipogenesis in adipocytes and its contribution to energy homeostasis and insulin sensitivity are less studied. Recent reports have gained significant insights into the signaling pathways that regulate lipogenic transcription factors and the role of DNL in adipose tissues. In this review, we will update the current knowledge of DNL in white and brown adipose tissues with the focus on transcriptional, post-translational, and central regulation of DNL. We will also summarize the recent findings of adipocyte DNL as a source of some signaling molecules that critically regulate energy metabolism.

Quinoline-Glycomimetic Conjugates Reducing Lipogenesis and Lipid Accumulation in Hepatocytes

Nonalcoholic fatty liver disease (NAFLD), which is characterized by excess accumulation of triglyceride in hepatocytes, is the major cause of chronic liver disease worldwide and no approved drug is available. The mechanistic target of rapamycin (mTOR) complexes has been implicated in promoting lipogenesis and fat accumulation in the liver, and thus, serve as attractive drug targets. The generation of non- or low cytotoxic mTOR inhibitors is required because existing cytotoxic mTOR inhibitors are not useful for NAFLD therapy. New compounds based on the privileged adenosine triphosphate (ATP) site binder quinoline scaffold conjugated to glucose and galactosamine derivatives, which have significantly low cytotoxicity, but strong mTORC1 inhibitory activity at low micromolar concentrations, have been synthesized. These compounds also effectively inhibit the rate of lipogenesis and lipid accumulation in cultured hepatocytes. This is the first report of glycomimetic-quinoline derivatives that reduce lipid load in hepatocytes.

Lipid metabolism reprogramming and its potential targets in cancer

Reprogramming of lipid metabolism is a newly recognized hallmark of malignancy. Increased lipid uptake, storage and lipogenesis occur in a variety of cancers and contribute to rapid tumor growth. Lipids constitute the basic structure of membranes and also function as signaling molecules and energy sources. Sterol regulatory element-binding proteins (SREBPs), a family of membrane-bound transcription factors in the endoplasmic reticulum, play a central role in the regulation of lipid metabolism. Recent studies have revealed that SREBPs are highly up-regulated in various cancers and promote tumor growth. SREBP cleavage-activating protein is a key transporter in the trafficking and activation of SREBPs as well as a critical glucose sensor, thus linking glucose metabolism and de novo lipid synthesis. Targeting altered lipid metabolic pathways has become a promising anti-cancer strategy. This review summarizes recent progress in our understanding of lipid metabolism regulation in malignancy, and highlights potential molecular targets and their inhibitors for cancer treatment.

Clusterin deficiency induces lipid accumulation and tissue damage in kidney

Clusterin is a secretory glycoprotein that is involved in multiple physiopathological processes, including lipid metabolism. Previous studies have shown that clusterin prevents hepatic lipid accumulation via suppression of sterol regulatory element-binding protein (SREBP) 1. In this study, we examined the role of clusterin in renal lipid accumulation in clusterin-knockout mice and NRK52e tubular epithelial cells. Clusterin deficiency increased the expression of SREBP1 and its target genes and decreased malonyl-CoA decarboxylase protein levels in the kidney. Expression of the endocytic receptor, megalin, and scavenger receptor class A was increased in clusterin-deficient mice. Functional analysis of lipid metabolism also revealed that lipid uptake and triglyceride synthesis were increased and fatty acid oxidation was reduced, leading to increased lipid accumulation in clusterin-deficient mice. These phenomena were accompanied by mesangial expansion, fibrosis and increased urinary protein-to-creatinine ratio. High-fat feeding aggravated these clusterin deficiency-induced pathological changes. Clusterin knockdown in NRK52e cells increased lipogenic gene expression and lipid levels, whereas overexpression of clusterin by treatment with adenovirus or recombinant clusterin protein suppressed lipogenic gene expression and lipid levels. Transforming growth factor-beta 1 (TGFB1) expression increased in the kidney of clusterin-deficient mice and suppression of TGFB1 in NRK52e cells suppressed lipid accumulation. These results suggest that clusterin deficiency induces renal lipid accumulation by dysregulating the expression of lipid metabolism-related factors and TGFB1, thereby leading to chronic kidney disease. Hence, clusterin may serve as a therapeutic target for lipid-induced chronic kidney disease.

The Role of Lipid Metabolism in T Lymphocyte Differentiation and Survival

The differentiation and effector functions of both the innate and adaptive immune system are inextricably linked to cellular metabolism. The features of metabolism which affect both arms of the immune system include metabolic substrate availability, expression of enzymes, transport proteins, and transcription factors which control catabolism of these substrates, and the ability to perform anabolic metabolism. The control of lipid metabolism is central to the appropriate differentiation and functions of T lymphocytes, and ultimately to the maintenance of immune tolerance. This review will focus on the role of fatty acid (FA) metabolism in T cell differentiation, effector function, and survival. FAs are important sources of cellular energy, stored as triglycerides. They are also used as precursors to produce complex lipids such as cholesterol and membrane phospholipids. FA residues also become incorporated into hormones and signaling moieties. FAs signal via nuclear receptors and their channeling, between storage as triacyl glycerides or oxidation as fuel, may play a role in survival or death of the cell. In recent years, progress in the field of immunometabolism has highlighted diverse roles for FA metabolism in CD4 and CD8 T cell differentiation and function. This review will firstly describe the sensing and modulation of the environmental FAs and lipid intracellular signaling and will then explore the key role of lipid metabolism in regulating the balance between potentially damaging pro-inflammatory and anti-inflammatory regulatory responses. Finally the complex role of extracellular FAs in determining cell survival will be discussed.

Association of genetic variations in the lipid regulatory pathway genes FBXW7 and SREBPs with coronary artery disease among Han Chinese and Uygur Chinese populations in Xinjiang, China

Background

Hyperlipidemia is a major risk factor for coronary artery disease (CAD). The current study was designed to explore the possible correlation between single nucleotide polymorphisms (SNPs) in the lipid homeostasis regulatory genes F-box and WD repeat domain-containing 7 (FBXW7) and sterol regulatory element-binding proteins (SREBPs) with CAD among Han Chinese and Uygur Chinese populations in Xinjiang, China.

Results

In the Uygur Chinese population, rs9902941 in SREBP-1 and rs10033601 in FBXW7 were found to be associated with CAD in a recessive model (TT vs. CT + CC, P = 0.032; GG vs. AG + AA, P = 0.010, respectively), and rs7288536 in SREBP-2 was found to be associated with CAD in an additive model (CT vs. CC + TT, P = 0.045). The difference was statistically significant in the Uygur Chinese population after multivariate adjustments [Odds ratio (OR) = 1.803, 95% confidence interval (CI): 1.036~3.137, P = 0.037; OR = 1.628, 95% CI: 1.080~2.454, P = 0.020; OR = 1.368; and 95% CI: 1.018~1.837, P = 0.037, respectively]. There were also significant interactions between the above-mentioned models in the Uygur Chinese population. However, these relationships were not observed before or after multivariate adjustment in the Han Chinese population.

Materials and Methods

A total of 1,312 Han Chinese (650 CAD patients and 662 controls) and 834 Uygur Chinese (414 CAD patients and 420 controls) were enrolled in this case-control study. Three SNPs (rs9902941 in SREBP-1, rs7288536 in SREBP-2 and rs10033601 in FBXW7) were selected and genotyped using the improved multiplex ligase detection reaction (iMLDR) method.

Conclusions

The results of this study indicate that variations in the lipid regulatory pathway genes FBXW7 and SREBPs (rs9902941 in SREBP-1, rs7288536 in SREBP-2 and rs10033601 in FBXW7) are associated with CAD in the Uygur Chinese population in Xinjiang, China.

Loss of Calreticulin Uncovers a Critical Role for Calcium in Regulating Cellular Lipid Homeostasis

A direct link between Ca²⁺ and lipid homeostasis has not been definitively demonstrated. In this study, we show that manipulation of ER Ca²⁺ causes the re-distribution of a portion of the intracellular unesterified cholesterol to a pool that is not available to the SCAP-SREBP complex. The SREBP processing pathway in ER Ca²⁺ depleted cells remained fully functional and responsive to changes in cellular cholesterol status but differed unexpectedly in basal activity. These findings establish the role of Ca²⁺ in determining the reference set-point for controlling cellular lipid homeostasis. We propose that ER Ca²⁺ status is an important determinant of the basal sensitivity of the sterol sensing mechanism inherent to the SREBP processing pathway.

Skin-specific regulation of SREBP processing and lipid biosynthesis by glycerol kinase 5

The recessive N-ethyl-N-nitrosourea-induced phenotype toku is characterized by delayed hair growth, progressive hair loss, and excessive accumulation of dermal cholesterol, triglycerides, and ceramides. The toku phenotype was attributed to a null allele of Gk5, encoding glycerol kinase 5 (GK5), a skin-specific kinase expressed predominantly in sebaceous glands. GK5 formed a complex with the sterol regulatory element-binding proteins (SREBPs) through their C-terminal regulatory domains, inhibiting SREBP processing and activation. In Gk5^toku/toku mice, transcriptionally active SREBPs accumulated in the skin, but not in the liver; they were localized to the nucleus and led to elevated lipid synthesis and subsequent hair growth defects. Similar defective hair growth was observed in kinase-inactive GK5 mutant mice. Hair growth defects of homozygous toku mice were partially rescued by treatment with the HMG-CoA reductase inhibitor simvastatin. GK5 exists as part of a skin-specific regulatory mechanism for cholesterol biosynthesis, independent of cholesterol regulation elsewhere in the body.

Genetic evidence for a role of the SREBP transcription system and lipid biosynthesis in schizophrenia and antipsychotic treatment

Schizophrenia is a serious psychotic disorder, with disabling symptoms and markedly reduced life expectancy. The onset is usually in late adolescence or early adulthood, which in time overlaps with the maturation of the brain including the myelination process. Interestingly, there seems to be a link between myelin abnormalities and schizophrenia. The oligodendrocyte-derived myelin membranes in the CNS are highly enriched for lipids (cholesterol, phospholipids and glycosphingolipids), thereby pointing at lipid homeostasis as a relevant target for studying the genetics and pathophysiology of schizophrenia. The biosynthesis of fatty acids and cholesterol is regulated by the sterol regulatory element binding protein (SREBP) transcription factors SREBP1 and SREBP2, which are encoded by the SREBF1 and SREBF2 genes on chromosome 17p11.2 and 22q13.2, respectively. Here we review the evidence for the involvement of SREBF1 and SREBF2 as genetic risk factors in schizophrenia and discuss the role of myelination and SREBP-mediated lipid biosynthesis in the etiology, pathophysiology and drug treatment of schizophrenia.

Dietary cholesterol interacts with SREBF1 to modulate obesity in Chinese children

SCOPE

Sterol regulatory element binding protein 1 gene (SREBF1) is an important candidate gene for obesity that could be affected by cholesterol. Different SREBF1 gene variants may have distinct responses to cholesterol, leading to different risks for obesity and obesity-related metabolic traits. Thus, we performed a gene-by-diet correlation analysis to test whether SREBF1 gene variation modulate the relationship between cholesterol and obesity.

METHODS AND RESULTS

A total of 642 school-aged children in Jinan, China, were selected by stratified cluster nested sampling. Anthropometric and biochemical measurements, as well as genotyping of tag single nucleotide polymorphisms (SNPs) of SREBF1, were performed in this sample. Nutritional intake assessments were completed using a 24-h dietary recall for three consecutive days. Multilevel mixed-effects linear regression was used to test interactions between SREBF1 SNPs and cholesterol intakes for obesity. Results showed that SREBF1 rs2236513/rs2297508/rs4925119 strongly modulated the relationship between cholesterol intake and serum LDL-cholesterol/total cholesterol levels (p < 0.001). While SREBF1 rs4925118 modulated the relationship between cholesterol intake and homeostasis model assessment of insulin resistance related characteristics (p < 0.05).

CONCLUSION

These results suggest that cholesterol intake recommendation may need to account for SREBF1 variation.

Transcriptional Regulation of Adipogenesis

Adipocytes are the defining cell type of adipose tissue. Once considered a passive participant in energy storage, adipose tissue is now recognized as a dynamic organ that contributes to several important physiological processes, such as lipid metabolism, systemic energy homeostasis, and whole-body insulin sensitivity. Therefore, understanding the mechanisms involved in its development and function is of great importance. Adipocyte differentiation is a highly orchestrated process which can vary between different fat depots as well as between the sexes. While hormones, miRNAs, cytoskeletal proteins, and many other effectors can modulate adipocyte development, the best understood regulators of adipogenesis are the transcription factors that inhibit or promote this process. Ectopic expression and knockdown approaches in cultured cells have been widely used to understand the contribution of transcription factors to adipocyte development, providing a basis for more sophisticated in vivo strategies to examine adipogenesis. To date, over two dozen transcription factors have been shown to play important roles in adipocyte development. These transcription factors belong to several families with many different DNA-binding domains. While peroxisome proliferator-activated receptor gamma (PPARγ) is undoubtedly the most important transcriptional modulator of adipocyte development in all types of adipose tissue, members of the CCAAT/enhancer-binding protein, Krüppel-like transcription factor, signal transducer and activator of transcription, GATA, early B cell factor, and interferon-regulatory factor families also regulate adipogenesis. The importance of PPARγ activity is underscored by several covalent modifications that modulate its activity and its ability to modulate adipocyte development. This review will primarily focus on the transcriptional control of adipogenesis in white fat cells and on the mechanisms involved in this fine-tuned developmental process. © 2017 American Physiological Society. Compr Physiol 7:635-674, 2017.

Regulation of Sterol Biosynthesis in the Human Fungal Pathogen Aspergillus fumigatus: Opportunities for Therapeutic Development

Sterols are a major component of eukaryotic cell membranes. For human fungal infections caused by the filamentous fungus Aspergillus fumigatus, antifungal drugs that target sterol biosynthesis and/or function remain the standard of care. Yet, an understanding of A. fumigatus sterol biosynthesis regulatory mechanisms remains an under developed therapeutic target. The critical role of sterol biosynthesis regulation and its interactions with clinically relevant azole drugs is highlighted by the basic helix loop helix (bHLH) class of transcription factors known as Sterol Regulatory Element Binding Proteins (SREBPs). SREBPs regulate transcription of key ergosterol biosynthesis genes in fungi including A. fumigatus. In addition, other emerging regulatory pathways and target genes involved in sterol biosynthesis and drug interactions provide additional opportunities including the unfolded protein response, iron responsive transcriptional networks, and chaperone proteins such as Hsp90. Thus, targeting molecular pathways critical for sterol biosynthesis regulation presents an opportunity to improve therapeutic options for the collection of diseases termed aspergillosis. This mini-review summarizes our current understanding of sterol biosynthesis regulation with a focus on mechanisms of transcriptional regulation by the SREBP family of transcription factors.

Cholesterol homeostasis: How do cells sense sterol excess?

Cholesterol is vital in mammals, but toxic in excess. Consequently, elaborate molecular mechanisms have evolved to maintain this sterol within narrow limits. How cells sense excess cholesterol is an intriguing area of research. Cells sense cholesterol, and other related sterols such as oxysterols or cholesterol synthesis intermediates, and respond to changing levels through several elegant mechanisms of feedback regulation. Cholesterol sensing involves both direct binding of sterols to the homeostatic machinery located in the endoplasmic reticulum (ER), and indirect effects elicited by sterol-dependent alteration of the physical properties of membranes. Here, we examine the mechanisms employed by cells to maintain cholesterol homeostasis.

The effects of PCB126 on intra-hepatic mechanisms associated with non alcoholic fatty liver disease

Background

Non alcoholic fatty liver disease (NAFLD) results from alteration in lipid synthesis and elimination mechanisms such as very-low density lipoprotein (VLDL) production and de novo lipogenesis. Persistent organic pollutants (POPs) are chemicals that were mostly used historically as pesticides, solvents, flame retardant, and other applications. Among POPs, polychlorinated biphenyls (PCB) have been recognized to be of environmental and potential toxicologic concerns. Specifically, PCB126 could act as endocrine disruptors and has recently been associated with hepatic fat accumulation. The purpose of the study was to investigate the effects of PCB126 on the molecular development of NAFLD using hepatocyte and rat models.

Methods

Hepatocytes were exposed to PCB 126 for 72 h and lipid accumulation in cells was quantified by Oil-Red-O. Rats were injected with a single dose of PCB126 or vehicle. Seven days later, liver triglycerides (TAG) content was measured along with protein quantification of hepatic microsomal triglyceride transfer protein (MTP), sterol regulatory element-binding protein 1c (SREBP1c) and diacylglycerol O-acyltransferase 2 (DGAT-2).

Results

Exposure to PCB126 resulted in significant increases of lipid accumulation in hepatocytes (38 %, P <0.05) and hepatic TAG concentrations (64 %, P <0.001) in rats compared to respective control groups. Rats with fatty livers depicted lower MTP (40 %, P <0.02), higher SREBP1c (27 %, P < 0.05) and DGAT-2 (120 %, P < 0.02) protein content levels compared to Placebo group in rats.

Conclusions

It seems that exposure to PCB126 has an important emerging role in the pathophysiology of NAFLD by 1) altering elimination mechanisms such as VLDL synthesis and secretion, through MTP; and 2) increasing hepatic TAG synthesis mechanisms through DGAT 2 and SREBP1c.

mTORC1 Down-Regulates Cyclin-Dependent Kinase 8 (CDK8) and Cyclin C (CycC)

In non-alcoholic fatty liver disease (NAFLD) and insulin resistance, hepatic de novo lipogenesis is often elevated, but the underlying mechanisms remain poorly understood. Recently, we show that CDK8 functions to suppress de novo lipogenesis. Here, we identify the mammalian target of rapamycin complex 1 (mTORC1) as a critical regulator of CDK8 and its activating partner CycC. Using pharmacologic and genetic approaches, we show that increased mTORC1 activation causes the reduction of the CDK8-CycC complex in vitro and in mouse liver in vivo. In addition, mTORC1 is more active in three mouse models of NAFLD, correlated with the lower abundance of the CDK8-CycC complex. Consistent with the inhibitory role of CDK8 on de novo lipogenesis, nuclear SREBP-1c proteins and lipogenic enzymes are accumulated in NAFLD models. Thus, our results suggest that mTORC1 activation in NAFLD and insulin resistance results in down-regulation of the CDK8-CycC complex and elevation of lipogenic protein expression.

Cholesterol and breast cancer pathophysiology

Cholesterol is a risk factor for breast cancer although the mechanisms by which this occurs are not well understood. One hypothesis is that dyslipidemia results in increased cholesterol content in cell membranes, thus impacting upon membrane fluidity and subsequent signaling. In addition, studies demonstrate that the metabolite, 27-hydroxycholesterol (27HC), can function as an estrogen, increasing the proliferation of estrogen receptor (ER)-positive breast cancer cells. This was unexpected because 27HC and other oxysterols activate the liver X receptors (LXR), resulting in a reduction of intracellular cholesterol. Resolution of this paradox will require dissection of the molecular mechanisms by which ER and LXR converge in breast cancer cells. Regardless, the observation that 27HC influences breast cancer provides a rationale for strategies that target cholesterol metabolism.

Phosphorylation of sterol regulatory element-binding protein (SREBP)-1c by p38 kinases, ERK and JNK influences lipid metabolism and the secretome of human liver cell line HepG2

The transcription factor sterol regulatory element binding protein (SREBP)-1c plays a pivotal role in lipid metabolism. In this report we identified the main phosphorylation sites of MAPK-families, i.e. p38 stress-activated MAPK (p38), ERK-MAPK (ERK) or c-JUN N-terminal protein kinases (JNK) in SREBP-1c. The major phosphorylation sites of p38, i.e. serine 39 and threonine 402, are identical to those we recently identified in the splice-variant SREBP-1a. In contrast, ERK and JNK phosphorylate SREBP-1c at two major sites, i.e. threonine 81 and serine 93, instead of one site in SREBP-1a. Functional analyses of the biological outcome in the human liver cell line HepG2 reveals SREBP-1c phosphorylation dependent alteration in lipid metabolism and secretion pattern of lipid transporting proteins, e.g. ApoE or ApoA1. These results suggest that phosphorylation of SREBP-1c by different MAPKs interferes with lipid metabolism and the secretory activity of liver cells.