SREBP-2, a second basic-helix-loop-helix-leucine zipper protein that stimulates transcription by binding to a sterol regulatory element

Dysregulated astrocyte cholesterol synthesis in Huntington's disease: A potential intersection with other cellular dysfunctions

Astrocytes are key elements for synapse development and function. Several astrocytic dysfunctions contribute to the pathophysiology of various neurodegenerative disorders, including Huntington's disease (HD), an autosomal-dominant neurodegenerative disorder that is characterized by motor and cognitive defects with behavioral/psychiatric disturbances. One dysfunction in HD related to astrocytes is reduced cholesterol synthesis, leading to a decreased availability of local cholesterol for synaptic activity. This review describes the specific role of astrocytes in the brain local cholesterol synthesis and presents evidence supporting a defective astrocyte-neuron cholesterol crosstalk in HD, by focusing on SREBP-2, the transcription factor that regulates the majority of genes involved in the cholesterol biosynthetic pathway. The emerging coordination of SREBP-2 with other physiological processes, such as energy metabolism, autophagy, and Sonic Hedgehog signaling, is also discussed. Finally, this review intends to stimulate future research directions to explore whether the impairment of astrocytic SREBP-2-mediated cholesterol synthesis in HD associates with other cellular dysfunctions in the disease.

Advances in plant oxygen sensing: endogenous and exogenous mechanisms

Oxygen is essential for the biochemical processes that sustain life in eukaryotic organisms. Although plants produce oxygen through photosynthesis, they often struggle to survive in low-oxygen environments, such as during flooding or submergence. To endure these conditions, they must reprogram their developmental and metabolic networks, and the adaptation process involves the continuous detection of both exogenous hypoxic signals and endogenous oxygen gradients. Recent research has significantly advanced our understanding of how plants respond to both endogenous and exogenous hypoxia signals. In this review, we explore advancements in both areas, comparing them to responses in animals, with a primary focus on how plants perceive and respond to exogenous hypoxic conditions, particularly those caused by flooding or submergence, as well as the hypoxia signaling pathways in different crops. Additionally, we discuss the interplay between endogenous and exogenous hypoxia signals in plants. Finally, we discuss future research directions aimed at improving crop resilience to flooding by integrating the perception and responses to both endogenous and exogenous signals. Through these efforts, we aspire to contribute to the development of crop varieties that are not only highly resistant but also experience minimal growth and yield penalties, thereby making substantial contributions to agricultural science.

SREBP2 as a central player in cancer progression: potential for targeted therapeutics

Recent studies have identified the reprogramming of lipid metabolism as a critical hallmark of malignancy. Enhanced cholesterol uptake and increased cholesterol biosynthesis significantly contribute to the rapid growth of tumors, with cholesterol also playing essential roles in cellular signaling pathways. Targeting cholesterol metabolism has emerged as a promising therapeutic strategy in oncology. The sterol regulatory element-binding protein-2 (SREBP2) serves as a primary transcriptional regulator of genes involved in cholesterol biosynthesis and is crucial for maintaining cholesterol homeostasis. Numerous studies have reported the upregulation of SREBP2 across various cancers, facilitating tumor progression. This review aims to provide a comprehensive overview of the structure, biological functions, and regulatory mechanisms of SREBP2. Furthermore, we summarize that SREBP2 plays a crucial role in various cancers and tumor microenvironment primarily by regulating cholesterol, as well as through several non-cholesterol pathways. We also particularly emphasize therapeutic agents targeting SREBP2 that are currently under investigation. This review seeks to enhance our understanding of SREBP2's involvement in cancer and provide theoretical references for cancer therapies that target SREBP2.

Pathways and Molecular Mechanisms Governing LDL Receptor Regulation

Clearance of circulating plasma LDL (low-density lipoprotein) cholesterol by the liver requires hepatic LDLR (low-density lipoprotein receptor). Complete absence of functional LDLR manifests in severe hypercholesterolemia and premature atherosclerotic cardiovascular disease. Since the discovery of the LDLR 50 years ago by Brown and Goldstein, all approved lipid-lowering medications have been aimed at increasing the abundance and availability of LDLR on the surface of hepatocytes to promote the removal of LDL particles from the circulation. As such a critical regulator of circulating and cellular cholesterol, it is not surprising that LDLR activity is tightly regulated. Despite over half a century's worth of study, there are still many facets of LDLR biology that remain unexplored. This review will focus on pathways that regulate the LDLR and emerging concepts of LDLR biology.

Targeting cholesterol metabolism: a promising therapy strategy for cancer

Cholesterol is a crucial structural component of cell membranes, playing a vital role in maintaining membrane fluidity and stability. Cholesterol metabolism involves four interconnected processes: de novo synthesis, uptake, efflux, and esterification. Disruptions in any of these pathways can lead to imbalances in cholesterol homeostasis, which are significantly associated with cancer progression. In recent years, traditional Chinese medicine (TCM) has emerged as a comprehensive therapeutic approach with multi-target and multi-pathway effects, demonstrating significant potential in regulating cholesterol metabolism. Research has shown that certain components of TCM can modulate enzymes, transport proteins, and signaling pathways involved in cholesterol metabolism, effectively interfering with survival and migration of cancer. These mechanisms highlight the unique advantages of TCM in inhibiting tumor progression. In this review we systematically describe the execution and regulation of the four key cholesterol metabolism processes, highlights the roles of critical proteins involved, and provides a comprehensive overview of natural products from TCM that modulate cholesterol metabolism. This review provides valuable insights for the development of novel drugs and cancer therapeutic strategies targeting cholesterol metabolism.

SLO co-opts host cell glycosphingolipids to access cholesterol-rich lipid rafts for enhanced pore formation and cytotoxicity

Streptolysin O (SLO) is a virulence determinant of group A Streptococcus (S. pyogenes), the agent of streptococcal sore throat and severe invasive infections. SLO is a member of a family of bacterial pore-forming toxins known as cholesterol-dependent cytolysins, which require cell membrane cholesterol for pore formation. While cholesterol is essential for cytolytic activity, accumulating data suggest that cell surface glycans may also participate in the binding of SLO and other cholesterol-dependent cytolysins to host cells. Here, we find that unbiased CRISPR screens for host susceptibility factors for SLO cytotoxicity identified genes encoding enzymes involved in the earliest steps of glycosphingolipid (GSL) biosynthesis. Targeted knockouts of these genes conferred relative resistance to SLO cytotoxicity in two independent human cell lines. Inactivation of ugcg, which codes for UDP-glucose ceramide glucosyltransferase, the enzyme catalyzing the first glycosylation step in GSL biosynthesis, reduced the clustering of SLO on the cell surface. This result suggests that binding to GSLs serves to cluster SLO molecules at lipid rafts where both GSLs and cholesterol are abundant. SLO clustering and susceptibility to SLO cytotoxicity were restored by reconstituting the GSL content of ugcg knockout cells with ganglioside GM1, but susceptibility to SLO cytotoxicity was not restored by a GM1 variant that lacks an oligosaccharide head group required for SLO binding, nor by a variant with a "kinked" acyl chain that prevents efficient packing of the ganglioside ceramide moiety with cholesterol. Thus, SLO appears to co-opt cell surface glycosphingolipids to gain access to lipid rafts for increased efficiency of pore formation and cytotoxicity.

IMPORTANCE

Group A Streptococcus is a global public health concern as it causes streptococcal sore throat and less common but potentially life-threatening invasive infections. Invasive infections have been associated with bacterial strains that produce large amounts of a secreted toxin, streptolysin O (SLO), which belongs to a family of pore-forming toxins produced by a variety of bacterial species. This study reveals that SLO binds to a class of molecules known as glycosphingolipids on the surface of human cells and that this interaction promotes efficient binding of SLO to cholesterol in the cell membrane and enhances pore formation. Understanding how SLO damages human cells provides new insight into streptococcal infection and may inform new approaches to treatment and prevention.

Dendrobium nobile Lindl. alkaloids improve lipid metabolism by increasing LDL uptake through regulation of the LXRα/IDOL/LDLR pathway and inhibition of PCSK9 expression in HepG2 cells

Dendrobium nobile Lindl. alkaloids (DNLA) are active ingredients that can be extracted from the traditional Chinese herb Dendrobium Nobile Lindl. DNLA exhibits hypoglycemic and antihyperlipidemia effects. However, to the best of our knowledge, the specific molecular mechanism by which DNLA can regulate lipid metabolism remains unclear. The aim of the present study was to investigate the effect of DNLA on lipopolysaccharide (LPS)-induced lipid metabolism in HepG2 cells and its potential mechanism. HepG2 cells were treated with LPS with or without different concentrations of DNLA (0, 0.035, 0.35 and 3.5 µg/ml) for 48 h. Cell viability was then detected using the Cell Counting Kit-8 assay. The 1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanideperchlorate-low-density lipoprotein (LDL) uptake assay was used to examine LDL uptake. In addition, possible mechanisms were explored using western blot analysis. The effect of the combination of DNLA with rosuvastatin calcium on the expression levels of the LDL receptor (LDLR) and proprotein convertase subtilisin/Kexin type 9 (PCSK9) was examined. The results indicated that LPS stimulation reduced the uptake of LDL by HepG2 cells, decreased the intracellular LDLR content, and increased the expression levels of inducible degrader of the LDLR (IDOL) and liver X receptor (LXR)α. DNLA intervention reversed all of the aforementioned LPS-induced effects in HepG2 cells. Additional mechanistic experiments revealed that DNLA exerted its effects mainly by regulating the LXRα/IDOL/LDLR pathway. It was shown that DNLA also reduced the expression levels of PCSK9, sterol regulatory element binding protein 2 and hepatocyte nuclear factor 1α. In addition, DNLA decreased the expression levels of PCSK9 in rosuvastatin calcium-induced HepG2 cells. Notably, DNLA was able to decrease 3-hydroxy-3-methylglutaryl-coenzyme A reductase and increase cytochrome p450 7A1 expression at the protein level, which are rate-limiting enzymes in cholesterol synthesis and metabolism. Collectively, these data suggested that DNLA could enhance LDL uptake of HepG2 cells by increasing LDLR expression through the LXRα/IDOL/LDLR pathway to alleviate the effects induced by LPS, suggesting the potential benefit of DNLA in improving lipid metabolism disorders.

Molecular Characteristics and Role of Buffalo SREBF2 in Triglyceride and Cholesterol Biosynthesis in Mammary Epithelial Cells

Background/Objectives: Sterol regulatory element-binding transcription factor 2 (SREBF2) is a key transcription factor involved in regulating cholesterol homeostasis. However, its role in buffalo mammary gland lipid metabolism remains unclear. Methods: To address this, we isolated and characterized the SREBF2 gene from buffalo mammary glands and performed an in-depth analysis of its molecular characteristics, tissue-specific expression, and functional roles in buffalo mammary epithelial cells (BuMECs). Additionally, we investigated the single nucleotide polymorphisms (SNPs) of SREBF2 in both river and swamp buffalo. Results: The coding sequence (CDS) of buffalo SREBF2 is 3327 bp long and encodes a protein of 1108 amino acid residues. Bioinformatics analysis revealed that the molecular characteristics of buffalo SREBF2 were highly similar across Bovidae species, with collinearity being observed among them. An expression profile analysis revealed that SREBF2 is expressed in all 11 tested tissues of buffalo, with its expression level in the mammary gland being higher during lactation than in the dry period. The knockdown of SREBF2 in BuMECs during lactation led to a significant reduction in the expression of genes involved in triglyceride (TAG) and cholesterol synthesis, including PI3K, AKT, mTOR, SREBF1, PPARG, INSIG1, ACACA, SCD, DGAT1, LPL, CD36, HMGCR, and SQLE. This knockdown led to a 23.53% and 94.56% reduction in TAG and cholesterol levels in BuMECs, respectively. In addition, a total of 22 SNPs were identified in both buffalo types, of which four non-synonymous substitutions (c.301G>C, c.304A>T, c.1240G>A, and c.2944G>A) were found exclusively in the SREBF2 CDS of swamp buffalo, and the assessment revealed that these substitutions had no impact on SREBF2 function. Conclusions: These findings emphasize the critical role of SREBF2 in regulating both triglyceride and cholesterol biosynthesis, providing valuable insights into its functions in buffalo mammary glands.

Chickpea defense against dual stresses of salt and Fusarium wilt is enhanced through selected bHLH transcription factors carrying the bHLH-MYC_N domain

The plant transcriptome varies between combined stresses and single stresses, and is regulated differentially by transcription factors. Therefore, understanding the complexities of plant interactions with pathogens in stressed soils is always a challenge. In chickpea, 197 CabHLH genes were newly identified. Expression of 28 defense-associated CabHLHs [individual and combined stresses of Fusarium oxysporum f. sp. ciceris (Foc) and salt (NaCl) in three chickpea cultivars (JG-315: wilt resistant, JG-36: wilt tolerant, and JG-62: wilt susceptible) in Trichoderma asperellum T42 primed and non-primed conditions] revealed upregulation of most CabHLHs at 12 h post-stress in individual stresses but decreased significantly in the combined stress (Foc and salt). However, T42 priming stimulated the transcript accumulation of most CabHLHs even earlier (6 h). Three genes (CabHLH119, 158, and 184 carrying an additional domain bHLH-MYC_N) and two additional genes (CabHLH69 and 172) belonging to the subfamilies IIIde and IIIf were upregulated significantly in all three cultivars under individual and combined stresses, and upregulated further when primed with T42. Expression of the three bHLH-MYC_N domain containing genes, and defense activities (PAL, PO activities, phenylpropanoid accumulation) in the combined stress correlated very strongly. Protein-protein interactome studies further strengthened the claim that the three bHLH-MYC_N domain carrying CabHLHs, is likely to regulate the defense signaling in chickpea under stress as they could form complexes either directly or indirectly with cis-elements of promoters of some important defense genes. The results thus showed the significance of the IIIde and IIIf subfamily genes, particularly those carrying the bHLH-MYC_N domain, in mitigating combined stresses.

Salmonella-induced cholesterol accumulation in infected macrophages suppresses autophagy via mTORC1 activation

Salmonella enterica serovar Typhimurium is a Gram-negative bacillus that infects the host intestinal epithelium and resident macrophages. Many intracellular pathogens induce an autophagic response in host cells but have evolved mechanisms to subvert that response. Autophagy is closely linked to cellular cholesterol levels; mTORC1 senses increased cholesterol in lysosomal membranes, leading to its hyperactivity and suppression of autophagy. Previous studies indicate that Salmonella infection induces dramatic accumulation of cholesterol in macrophages, a fraction of which localizes to Salmonella containing vacuoles (SCVs). We previously reported that the bacterial effector protein SseJ triggers cholesterol accumulation through a signaling cascade involving focal adhesion kinase (FAK) and Akt. Here we show that mTORC1 is recruited to SCVs and is hyperactivated in a cholesterol-dependent manner. If cholesterol accumulation is prevented pharmacologically or through mutation of sseJ, autophagy is induced and bacterial survival is attenuated. Notably, the host lipid transfer protein OSBP (oxysterol binding protein 1) is also recruited to SCVs and its activity is necessary for both cholesterol transfer to SCVs and mTORC1 activation during infection. Finally, lipidomic analysis of Salmonella-infected macrophages revealed new insights into how Salmonella may manipulate lipid homeostasis to benefit its survival. We propose that S. Typhimurium induces cholesterol accumulation through SseJ to activate mTORC1, preventing autophagic clearance of bacteria.

Toxoplasma gondii sustains survival by regulating cholesterol biosynthesis and uptake via SREBP2 activation

Toxoplasma gondii (T. gondii) is an obligate intracellular parasite that cannot biosynthesize cholesterol via the mevalonate pathway, it sources this lipid from its host. We discovered that T. gondii infection upregulated the expression of host cholesterol synthesis-related genes HMG-CoA reductase(HMGCR), squalene epoxidase (SQLE), and dehydrocholesterol reductase-7 (DHCR7), and increased the uptake pathway gene low-density lipoprotein receptor (LDLR). We found a protein, sterol regulatory element binding protein 2 (SREBP2), which is the key protein regulating the host cholesterol synthesis and uptake during T. gondii infection. T. gondii induced a dose-dependent nuclear translocation of SREBP2. Knockdown SREBP2 reduced T. gondii-induced cholesterol biosynthesis and uptake. Consequently, the parasite's ability to acquire cholesterol was significantly diminished, impairing its invasion, replication, and bradyzoites development. Interfering cholesterol metabolism using AY9944 effectively inhibited T. gondii replication. In summary, SREBP2 played an important role in T. gondii infection in vitro, serving as a potential target for regulating T. gondii-induced cholesterol metabolism, offering insights into the prevention and treatment of toxoplasmosis.

Roles of posttranslational modifications in lipid metabolism and cancer progression

Lipid metabolism reprogramming has emerged as a hallmark of malignant tumors. Lipids represent a complex group of biomolecules that not only compose the essential components of biological membranes and act as an energy source, but also function as messengers to integrate various signaling pathways. In tumor cells, de novo lipogenesis plays a crucial role in acquiring lipids to meet the demands of rapid growth. Increasing evidence has suggested that dysregulated lipid metabolism serves as a driver of cancer progression. Posttranslational modifications (PTMs), which occurs in most eukaryotic proteins throughout their lifetimes, affect the activity, abundance, function, localization, and interactions of target proteins. PTMs of crucial molecules are potential intervention sites and are emerging as promising strategies for the cancer treatment. However, there is limited information available regarding the PTMs that occur in cancer lipid metabolism and the potential treatment strategies associated with these PTMs. Herein, we summarize current knowledge of the roles and regulatory mechanisms of PTMs in lipid metabolism. Understanding the roles of PTMs in lipid metabolism in cancer could provide valuable insights into tumorigenesis and progression. Moreover, targeting PTMs in cancer lipid metabolism might represent a promising novel therapeutic strategy.

SPRING is a Dedicated Licensing Factor for SREBP-Specific Activation by S1P

SREBP transcription factors are central regulators of lipid metabolism. Their proteolytic activation requires ER to the Golgi translocation and subsequent cleavage by site-1-protease (S1P). Produced as a proprotein, S1P undergoes autocatalytic cleavage from its precursor S1PA to mature S1PC form. Here, we report that SPRING (previously C12ORF29) and S1P interact through their ectodomains, and that this facilitates the autocatalytic cleavage of S1PA into its mature S1PC form. Reciprocally, we identified a S1P recognition-motif in SPRING and demonstrate that S1P-mediated cleavage leads to secretion of the SPRING ectodomain in cells, and in liver-specific Spring knockout (LKO) mice transduced with AAV-mSpring. By reconstituting SPRING variants into SPRINGKO cells we show that the SPRING ectodomain supports proteolytic maturation of S1P and SREBP signaling, but that S1P-mediated SPRING cleavage is not essential for these processes. Absence of SPRING modestly diminishes proteolytic maturation of S1PA→C and trafficking of S1PC to the Golgi. However, despite reaching the Golgi in SPRINGKO cells, S1PC fails to rescue SREBP signaling. Remarkably, whereas SREBP signaling was severely attenuated in SPRINGKO cells and LKO mice, that of ATF6, another S1P substrate, was unaffected in these models. Collectively, our study positions SPRING as a dedicated licensing factor for SREBP-specific activation by S1P.

Characterization and expression analysis of seven lipid metabolism-related genes in yellow catfish Pelteobagrus fulvidraco fed high fat and bile acid diet

SREBPs, such as SREBP1 and SREBP2, were the key transcriptional factors regulating lipid metabolism. The processing of SREBPs involved many genes, such as scap, s1p, s2p, cideb. Here, we deciphered the full-length cDNA sequences of scap, srebp1, srebp2, s1p, s2p, cideb and cidec from yellow catfish Pelteobagrus fulvidraco. Their full-length cDNA sequences ranged from 1587 to 3884 bp, and their ORF length from 1191 to 2979 bp, encoding 396-992 amino acids. Some conservative domains were predicted, including the multiple transmembrane domains in SCAP, the bHLH-ZIP domain in SREBP1 and SREBP2, the ApoB binding region, ER targeting region and LD targeting region in CIDEb, the LD targeting region in the CIDEc, the conserved catalytic site and processing site in S1P, and the transmembrane helix domain in S2P. Their mRNA expression could be observed in the heart, spleen, liver, kidney, brain, muscle, intestine and adipose, but varied with tissues. The changes of their mRNA expression in responses to high-fat (HFD) and bile acid (BA) diets were also investigated in the brain, heart, intestine, kidney and spleen tissues. In the brain, HFD significantly increased the mRNA expression of seven genes (scap, srebp1, srebp2, s1p, s2p, cideb and cidec), and the BA attenuated the increase of scap, srebp1, srebp2, s1p, s2p, cideb and cidec mRNA expression induced by HFD. In the heart, HFD significantly increased the mRNA abundances of six genes (srebp1, srebp2, scap, s2p, cideb and cidec), and BA attenuated the increase of their mRNA abundances induced by HFD. In the intestine, HFD increased the cideb, s1p and s2p mRNA abundances, and BA attenuated the HFD-induced increment of their mRNA abundances. In the kidney, HFD significantly increased the scap, cidec and s1p mRNA expression, and BA diet attenuated the increment of their mRNA expression. In the spleen, HFD treatment increased the scap, srebp2, s1p and s2p mRNA expression, and BA diet attenuated HFD-induced increment of their mRNA expression. Taken together, our study elucidated the characterization, expression profiles and transcriptional response of seven lipid metabolic genes, which would serve as the good basis for the further exploration into their function and regulatory mechanism in fish.

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.

Finishing the egg

Gamete development is a fundamental process that is highly conserved from early eukaryotes to mammals. As germ cells develop, they must coordinate a dynamic series of cellular processes that support growth, cell specification, patterning, the loading of maternal factors (RNAs, proteins, and nutrients), differentiation of structures to enable fertilization and ensure embryonic survival, and other processes that make a functional oocyte. To achieve these goals, germ cells integrate a complex milieu of environmental and developmental signals to produce fertilizable eggs. Over the past 50 years, Drosophila oogenesis has risen to the forefront as a system to interrogate the sophisticated mechanisms that drive oocyte development. Studies in Drosophila have defined mechanisms in germ cells that control meiosis, protect genome integrity, facilitate mRNA trafficking, and support the maternal loading of nutrients. Work in this system has provided key insights into the mechanisms that establish egg chamber polarity and patterning as well as the mechanisms that drive ovulation and egg activation. Using the power of Drosophila genetics, the field has begun to define the molecular mechanisms that coordinate environmental stresses and nutrient availability with oocyte development. Importantly, the majority of these reproductive mechanisms are highly conserved throughout evolution, and many play critical roles in the development of somatic tissues as well. In this chapter, we summarize the recent progress in several key areas that impact egg chamber development and ovulation. First, we discuss the mechanisms that drive nutrient storage and trafficking during oocyte maturation and vitellogenesis. Second, we examine the processes that regulate follicle cell patterning and how that patterning impacts the construction of the egg shell and the establishment of embryonic polarity. Finally, we examine regulatory factors that control ovulation, egg activation, and successful fertilization.

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.

Getting to Grips with the Oxysterol-Binding Protein Family - a Forty Year Perspective

This review discusses how research around the oxysterol-binding protein family has evolved. We briefly summarize how this protein family, designated OSBP-related (ORP) or OSBP-like (OSBPL) proteins, was discovered, how protein domains highly conserved among family members between taxa paved the way for understanding their mechanisms of action, and how insights into protein structural and functional features help to understand their versatility as lipid transporters. We also discuss questions and future avenues of research opened by these findings. The investigations on oxysterol-binding protein family serve as a real-life example of the notion that science often advances as a collective effort of multiple lines of enquiry, including serendipitous routes. While original articles invariably explain the motivation of the research undertaken in rational terms, the actual paths to findings may be less intentional. Fortunately, this does not reduce the impact of the discoveries made. Besides hopefully providing a useful account of ORP family proteins, we aim to convey this message.

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.

Competing endogenous RNAs in human astrocytes: crosstalk and interacting networks in response to lipotoxicity

Neurodegenerative diseases (NDs) are characterized by a progressive deterioration of neuronal function, leading to motor and cognitive damage in patients. Astrocytes are essential for maintaining brain homeostasis, and their functional impairment is increasingly recognized as central to the etiology of various NDs. Such impairment can be induced by toxic insults with palmitic acid (PA), a common fatty acid, that disrupts autophagy, increases reactive oxygen species, and triggers inflammation. Although the effects of PA on astrocytes have been addressed, most aspects of the dynamics of this fatty acid remain unknown. Additionally, there is still no model that satisfactorily explains how astroglia goes from being neuroprotective to neurotoxic. Current incomplete knowledge needs to be improved by the growing field of non-coding RNAs (ncRNAs), which is proven to be related to NDs, where the complexity of the interactions among these molecules and how they control other RNA expressions need to be addressed. In the present study, we present an extensive competing endogenous RNA (ceRNA) network using transcriptomic data from normal human astrocyte (NHA) cells exposed to PA lipotoxic conditions and experimentally validated data on ncRNA interaction. The obtained network contains 7 lncRNA transcripts, 38 miRNAs, and 239 mRNAs that showed enrichment in ND-related processes, such as fatty acid metabolism and biosynthesis, FoxO and TGF-β signaling pathways, prion diseases, apoptosis, and immune-related pathways. In addition, the transcriptomic profile was used to propose 22 potential key controllers lncRNA/miRNA/mRNA axes in ND mechanisms. The relevance of five of these axes was corroborated by the miRNA expression data obtained in other studies. MEG3 (ENST00000398461)/hsa-let-7d-5p/ATF6B axis showed importance in Parkinson's and late Alzheimer's diseases, while AC092687.3/hsa-let-7e-5p/[SREBF2, FNIP1, PMAIP1] and SDCBP2-AS1 (ENST00000446423)/hsa-miR-101-3p/MAPK6 axes are probably related to Alzheimer's disease development and pathology. The presented network and axes will help to understand the PA-induced mechanisms in astrocytes, leading to protection or injury in the CNS under lipotoxic conditions as part of the intricated cellular regulation influencing the pathology of different NDs. Furthermore, the five corroborated axes could be considered study targets for new pharmacologic treatments or as possible diagnostic molecules, contributing to improving the quality of life of millions worldwide.

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.

A new SPRING in lipid metabolism

PURPOSE OF REVIEW

The SREBP transcription factors are master regulators of lipid homeostasis owing to their role in controlling cholesterol and fatty acid metabolism. The core machinery required to promote their trafficking and proteolytic activation has been established close to 20 years ago. In this review, we summarize the current understanding of a newly identified regulator of SREBP signaling, SPRING (formerly C12ORF49), its proposed mechanism of action, and its role in lipid metabolism.

RECENT FINDINGS

Using whole-genome functional genetic screens we, and others, have recently identified SPRING as a novel regulator of SREBP signaling. SPRING is a Golgi-resident single-pass transmembrane protein that is required for proteolytic activation of SREBPs in this compartment. Mechanistic studies identified regulation of S1P, the protease that cleaves SREBPs, and control of retrograde trafficking of the SREBP chaperone SCAP from the Golgi to the ER as processes requiring SPRING. Emerging studies suggest an important role for SPRING in regulating circulating and hepatic lipid levels in mice and potentially in humans.

SUMMARY

Current studies support the notion that SPRING is a novel component of the core SREBP-activating machinery. Additional studies are warranted to elucidate its role in cellular and systemic lipid metabolism.

The translational potential of cholesterol-based therapies for neurological disease

Cholesterol is an important metabolite and membrane component and is enriched in the brain owing to its role in neuronal maturation and function. In the adult brain, cholesterol is produced locally, predominantly by astrocytes. When cholesterol has been used, recycled and catabolized, the derivatives are excreted across the blood-brain barrier. Abnormalities in any of these steps can lead to neurological dysfunction. Here, we examine how precise interactions between cholesterol production and its use and catabolism in neurons ensures cholesterol homeostasis to support brain function. As an example of a neurological disease associated with cholesterol dyshomeostasis, we summarize evidence from animal models of Huntington disease (HD), which demonstrate a marked reduction in cholesterol biosynthesis with clinically relevant consequences for synaptic activity and cognition. In addition, we examine the relationship between cholesterol loss in the brain and cognitive decline in ageing. We then present emerging therapeutic strategies to restore cholesterol homeostasis, focusing on evidence from HD mouse models.

Functional significance of cholesterol metabolism in cancer: from threat to treatment

Cholesterol is an essential structural component of membranes that contributes to membrane integrity and fluidity. Cholesterol homeostasis plays a critical role in the maintenance of cellular activities. Recently, increasing evidence has indicated that cholesterol is a major determinant by modulating cell signaling events governing the hallmarks of cancer. Numerous studies have shown the functional significance of cholesterol metabolism in tumorigenesis, cancer progression and metastasis through its regulatory effects on the immune response, ferroptosis, autophagy, cell stemness, and the DNA damage response. Here, we summarize recent literature describing cholesterol metabolism in cancer cells, including the cholesterol metabolism pathways and the mutual regulatory mechanisms involved in cancer progression and cholesterol metabolism. We also discuss various drugs targeting cholesterol metabolism to suggest new strategies for cancer treatment.

Effect of the JAK/STAT Inhibitor Tofacitinib on Macrophage Cholesterol Metabolism

The impact of JAK/STAT inhibitors, which are used in various inflammatory diseases, on cardiovascular risk is controversial and has recently raised safety concerns. Our study investigates the direct effects of tofacitinib on macrophage cholesterol metabolism, which is crucial for atherosclerosis plaque development and stability. Cultured human macrophages THP-1 were used to assess the impact of tofacitinib on cell cholesterol efflux and synthesis via radioisotopic methods, and on cholesterol uptake by measuring the cell cholesterol content with a fluorometric assay. The cholesterol acceptors and donors were either standard lipoproteins or sera from patients with juvenile idiopathic arthritis (JIA) and from control subjects. Tofacitinib significantly increased the macrophage cholesterol efflux to all acceptors; it reduced cholesterol uptake from both the normal and hypercholesterolemic sera; and it reduced cholesterol synthesis. The treatment of macrophages with tofacitinib was able to increase the cholesterol efflux and decrease cholesterol uptake when using sera from untreated JIA patients with active disease as cholesterol acceptors and donors, respectively. In conclusion, our in vitro data support the concept that tofacitinib has a favorable impact on macrophage cholesterol metabolism, even in the presence of sera from rheumatologic patients, and suggest that other mechanisms may be responsible for the cardiovascular risk associated with tofacitinib use in selected patient populations.

Decoding the crosstalk between mevalonate metabolism and T cell function

The mevalonate pathway is an essential metabolic pathway in T cells regulating development, proliferation, survival, differentiation, and effector functions. The mevalonate pathway is a complex, branched pathway composed of many enzymes that ultimately generate cholesterol and nonsterol isoprenoids. T cells must tightly control metabolic flux through the branches of the mevalonate pathway to ensure sufficient isoprenoids and cholesterol are available to meet cellular demands. Unbalanced metabolite flux through the sterol or the nonsterol isoprenoid branch is metabolically inefficient and can have deleterious consequences for T cell fate and function. Accordingly, there is tight regulatory control over metabolic flux through the branches of this essential lipid synthetic pathway. In this review we provide an overview of how the branches of the mevalonate pathway are regulated in T cells and discuss our current understanding of the relationship between mevalonate metabolism, cholesterol homeostasis and T cell function.

The Molecular and Genetic Interactions between Obesity and Breast Cancer Risk

Breast cancer (BC) is considered the leading cause of death among females worldwide. Various risk factors contribute to BC development, such as age, genetics, reproductive factors, obesity, alcohol intake, and lifestyle. Obesity is considered to be a pandemic health problem globally, affecting millions of people worldwide. Obesity has been associated with a high risk of BC development. Determining the impact of obesity on BC development risk in women by demonstrating the molecular and genetic association in pre- and post-menopause females and risk to BC initiation is crucial in order to improve the diagnosis and prognosis of BC disease. In epidemiological studies, BC in premenopausal women was shown to be protective in a certain pattern. These altered effects between the two phases could be due to various physiological changes, such as estrogen/progesterone fluctuating levels. In addition, the relationship between BC risk and obesity is indicated by different molecular alterations as metabolic pathways and genetic mutation or epigenetic DNA changes supporting a strong connection between obesity and BC risk. However, these molecular and genetic alteration remain incompletely understood. The aim of this review is to highlight and elucidate the different molecular mechanisms and genetic changes occurring in obese women and their association with BC risk and development.

Physiological and pathological roles of lipogenesis

Lipids are essential metabolites, which function as energy sources, structural components and signalling mediators. Most cells are able to convert carbohydrates into fatty acids, which are often converted into neutral lipids for storage in the form of lipid droplets. Accumulating evidence suggests that lipogenesis plays a crucial role not only in metabolic tissues for systemic energy homoeostasis but also in immune and nervous systems for their proliferation, differentiation and even pathophysiological roles. Thus, excessive or insufficient lipogenesis is closely associated with aberrations in lipid homoeostasis, potentially leading to pathological consequences, such as dyslipidaemia, diabetes, fatty liver, autoimmune diseases, neurodegenerative diseases and cancers. For systemic energy homoeostasis, multiple enzymes involved in lipogenesis are tightly controlled by transcriptional and post-translational modifications. In this Review, we discuss recent findings regarding the regulatory mechanisms, physiological roles and pathological importance of lipogenesis in multiple tissues such as adipose tissue and the liver, as well as the immune and nervous systems. Furthermore, we briefly introduce the therapeutic implications of lipogenesis modulation.

Pathogenic mechanisms and regulatory factors involved in alcoholic liver disease

Alcoholism is a widespread and damaging behaviour of people throughout the world. Long-term alcohol consumption has resulted in alcoholic liver disease (ALD) being the leading cause of chronic liver disease. Many metabolic enzymes, including alcohol dehydrogenases such as ADH, CYP2E1, and CATacetaldehyde dehydrogenases ALDHsand nonoxidative metabolizing enzymes such as SULT, UGT, and FAEES, are involved in the metabolism of ethanol, the main component in alcoholic beverages. Ethanol consumption changes the functional or expression profiles of various regulatory factors, such as kinases, transcription factors, and microRNAs. Therefore, the underlying mechanisms of ALD are complex, involving inflammation, mitochondrial damage, endoplasmic reticulum stress, nitrification, and oxidative stress. Moreover, recent evidence has demonstrated that the gut-liver axis plays a critical role in ALD pathogenesis. For example, ethanol damages the intestinal barrier, resulting in the release of endotoxins and alterations in intestinal flora content and bile acid metabolism. However, ALD therapies show low effectiveness. Therefore, this review summarizes ethanol metabolism pathways and highly influential pathogenic mechanisms and regulatory factors involved in ALD pathology with the aim of new therapeutic insights.

DAXX drives de novo lipogenesis and contributes to tumorigenesis

Cancer cells exhibit elevated lipid synthesis. In breast and other cancer types, genes involved in lipid production are highly upregulated, but the mechanisms that control their expression remain poorly understood. Using integrated transcriptomic, lipidomic, and molecular studies, here we report that DAXX is a regulator of oncogenic lipogenesis. DAXX depletion attenuates, while its overexpression enhances, lipogenic gene expression, lipogenesis, and tumor growth. Mechanistically, DAXX interacts with SREBP1 and SREBP2 and activates SREBP-mediated transcription. DAXX associates with lipogenic gene promoters through SREBPs. Underscoring the critical roles for the DAXX-SREBP interaction for lipogenesis, SREBP2 knockdown attenuates tumor growth in cells with DAXX overexpression, and DAXX mutants unable to bind SREBP1/2 have weakened activity in promoting lipogenesis and tumor growth. Remarkably, a DAXX mutant deficient of SUMO-binding fails to activate SREBP1/2 and lipogenesis due to impaired SREBP binding and chromatin recruitment and is defective of stimulating tumorigenesis. Hence, DAXX's SUMO-binding activity is critical to oncogenic lipogenesis. Notably, a peptide corresponding to DAXX's C-terminal SUMO-interacting motif (SIM2) is cell-membrane permeable, disrupts the DAXX-SREBP1/2 interactions, and inhibits lipogenesis and tumor growth. These results establish DAXX as a regulator of lipogenesis and a potential therapeutic target for cancer therapy.

Lipid Metabolic Reprogramming in Embryonal Neoplasms with MYCN Amplification

Tumor cells reprogram their metabolism, including glucose, glutamine, nucleotide, lipid, and amino acids to meet their enhanced energy demands, redox balance, and requirement of biosynthetic substrates for uncontrolled cell proliferation. Altered lipid metabolism in cancer provides lipids for rapid membrane biogenesis, generates the energy required for unrestricted cell proliferation, and some of the lipids act as signaling pathway mediators. In this review, we focus on the role of lipid metabolism in embryonal neoplasms with MYCN dysregulation. We specifically review lipid metabolic reactions in neuroblastoma, retinoblastoma, medulloblastoma, Wilms tumor, and rhabdomyosarcoma and the possibility of targeting lipid metabolism. Additionally, the regulation of lipid metabolism by the MYCN oncogene is discussed.

Roles of Cholesterol and PtdIns(4,5)P2 in the Regulation of STIM1-Orai1 Channel Function

Calcium is one of the most prominent second messengers. It is involved in a wide range of functions at the single-cell level but also in modulating regulatory mechanisms in the entire organism. One process mediating calcium signaling involves hydrolysis of phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P₂) by the phospholipase-C (PLC). Thus, calcium and PtdIns(4,5)P₂ are intimately intertwined two second-messenger cascades that often depend on each other. Another relevant lipid associated with calcium signaling is cholesterol. Both PtdIns(4,5)P₂ and cholesterol play key roles in the formation and maintenance of specialized signaling nanodomains known as lipid rafts. Lipid rafts are particularly important in calcium signaling by concentrating and localizing calcium channels such as the Orai1 channel. Depletion of internal calcium stores is initiated by the production of inositol-1,4,5-trisphosphate (IP3). Calcium depletion from the ER induces the oligomerization of STIM1, which binds Orai1 and initiates calcium influx into the cell. In the present review, we analyzed the complex interactions between cholesterol, PtdIns(4,5)P₂, and the complex formed by the Orai1 channel and the signaling molecule STIM1. We explore some of the complex mechanisms governing calcium homeostasis and phospholipid metabolism, as well as the interaction between these two apparently independent signaling cascades.

Enhanced CHOLESTEROL biosynthesis promotes breast cancer metastasis via modulating CCDC25 expression and neutrophil extracellular traps formation

Neutrophil extracellular traps (NETs) has been demonstrated to regulate the metastasis of breast cancer. In this study, we showed that de novo cholesterol biosynthesis induced by ASPP2 depletion in mouse breast cancer cell 4T1 and human breast cancer cell MDA-MB-231 promoted NETs formation in vitro, as well as in lung metastases in mice intravenously injected with ASPP2-deficient 4T1 cells. Simvastatin and berberine (BBR), cholesterol synthesis inhibitors, efficiently blocked ASPP2-depletion induced NETs formation. Cholesterol biosynthesis greatly enhanced Coiled-coil domain containing protein 25 (CCDC25) expression on cancer cells as well as in lung metastases. CCDC25 expression was co-localized with caveolin-1, a lipid raft molecule, and was damped by inhibitor of lipid rafts formation. Our data suggest that cholesterol biosynthesis promotes CCDC25 expression in a lipid raft-dependent manner. Clinically, the expression of CCDC25 was positively correlated with the expression of 3-hydroxy-3-methylglutaryl-CoAreductase (HMRCG), and citrullinated histone H3 (H3cit), in tissues from breast cancer patients. High expression of CCDC25 and HMGCR was related with worse prognosis in breast cancer patients. In conclusion, our study explores a novel mechanism for de novo cholesterol biosynthesis in the regulation of CCDC25 expression, NETs formation and breast cancer metastasis. Targeting cholesterol biosynthesis may be promising therapeutic strategies to treat breast cancer metastasis.

ZMYND8 is a master regulator of 27-hydroxycholesterol that promotes tumorigenicity of breast cancer stem cells

27-Hydroxycholesterol (27-HC) is the most abundant oxysterol that increases the risk of breast cancer progression. However, little is known about epigenetic regulation of 27-HC metabolism and its role in breast tumor initiation. Using genetic mouse mammary tumor and human breast cancer models, we showed here that the histone reader ZMYND8 was selectively expressed in breast cancer stem cells (BCSCs) and promoted epithelial-mesenchymal transition (EMT), BCSC maintenance and self-renewal, and oncogenic transformation through its epigenetic functions, leading to breast tumor initiation. Mechanistically, ZMYND8 was a master transcriptional regulator of 27-HC metabolism. It increased cholesterol biosynthesis and oxidation but blocked cholesterol efflux and 27-HC catabolism, leading to accumulation of 27-HC in BCSCs. Consequently, 27-HC promoted EMT, oncogenic transformation, and tumor initiation through activation of liver X receptor. These findings reveal that ZMYND8 is an epigenetic booster that drives breast tumor initiation through metabolic reprogramming.

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.

Studies in the antiviral molecular mechanisms of 25-hydroxycholesterol: Disturbing cholesterol homeostasis and post-translational modification of proteins

Efficient antiviral drug discovery has been a pressing issue of global public health concern since the outbreak of coronavirus disease 2019. In recent years, numerous in vitro and in vivo studies have shown that 25-hydroxycholesterol (25HC), a reactive oxysterol catalyzed by cholesterol-25-hydroxylase, exerts broad-spectrum antiviral activity with high efficiency and low toxicity. 25HC restricts viral internalization and disturbs the maturity of viral proteins using multiple mechanisms. First, 25HC reduces lipid rafts and cholesterol in the cytomembrane by inhibiting sterol-regulatory element binding proteins-2, stimulating liver X receptor, and activating Acyl-coenzyme A: cholesterol acyl-transferase. Second, 25HC impairs endosomal pathways by restricting the function of oxysterol-binding protein or Niemann-pick protein C1, causing the virus to fail to release nucleic acid. Third, 25HC disturbs the prenylation of viral proteins by suppressing the sterol-regulatory element binding protein pathway and glycosylation by increasing the sensitivity of glycans to endoglycosidase. This paper reviews previous studies on the antiviral activity of 25HC in order to fully understand its role in innate immunity and how it may contribute to the development of urgently needed broad-spectrum antiviral drugs.

The constellation of cholesterol-dependent processes associated with SARS-CoV-2 infection

The role of cholesterol in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and other coronavirus-host cell interactions is currently being discussed in the context of two main scenarios: i) the presence of the neutral lipid in cholesterol-rich lipid domains involved in different steps of the viral infection and ii) the alteration of metabolic pathways by the virus over the course of infection. Cholesterol-enriched lipid domains have been reported to occur in the lipid envelope membrane of the virus, in the host-cell plasma membrane, as well as in endosomal and other intracellular membrane cellular compartments. These membrane subdomains, whose chemical and physical properties distinguish them from the bulk lipid bilayer, have been purported to participate in diverse phenomena, from virus-host cell fusion to intracellular trafficking and exit of the virions from the infected cell. SARS-CoV-2 recruits many key proteins that participate under physiological conditions in cholesterol and lipid metabolism in general. This review analyses the status of cholesterol and lipidome proteins in SARS-CoV-2 infection and the new horizons they open for therapeutic intervention.

Form of dietary selenium affects mRNA encoding cholesterol biosynthesis and immune response elements in the early luteal phase bovine corpus luteum

Widespread regions of the southeast United States have soils, and hence forages, deficient in selenium (Se), necessitating Se supplementation to grazing cattle for optimal immune function, growth, and fertility. We have reported that supplementation with an isomolar 1:1 mix (MIX) of inorganic (ISe) and organic (OSe) forms of Se increases early luteal phase (LP) progesterone (P4) above that in cows on ISe alone. Increased early LP P4 advances embryonic development. Our objective was to determine the effect of form of Se on the transcriptome of the early LP corpus luteum (CL) with the goal of elucidating form of Se-regulated processes affecting luteal steroidogenesis and function. Non-lactating, 3-yr-old Angus-cross cows underwent 45-d Se-depletion, then repletion periods, and then at least 90 d of supplementation (TRT) with 35 ppm Se/d as either ISe (n = 5) or MIX (n = 5). CL were then recovered on day 7 of the estrous cycle, total RNA isolated, and the effect of TRT on the luteal transcriptome evaluated using bovine gene 1.0 ST arrays (Affymetrix, Inc., Santa Clara, CA). The abundance of transcripts in each CL was subjected to one-way ANOVA using Partek Genomic Suite software to determine TRT effects. Microarray analysis indicated a total of 887 transcripts that were differentially expressed and functionally annotated, with 423 and 464 up- and down-regulated (P < 0.05) in MIX vs. ISe CL, respectively. Bioinformatic analysis (Ingenuity Pathway Analysis) revealed the top TRT-affected canonical pathways to include seven specific to cholesterol biosynthesis and two to inflammatory responses. Results from the microarray analysis were corroborated by targeted real-time PCR. MIX CL had increased (P < 0.05) abundance of transcripts regulating cholesterol biosynthesis including DHCR7, DHCR24, and CYP51A1 (fold changes of 1.65, 1.48, and 1.40, respectively), suggesting MIX-induced increases in P4 to be due, in part, to increased availability of substrate to luteal cells. In addition, MIX CL had increased (P < 0.05) abundance of immune-response transcripts including C1QC, FAS, ILR8B, and IL1R1 (fold changes of 2.30, 1.74, 1.66, and 1.63, respectively). SREBF1 mRNA was also increased (1.32-fold, P < 0.05) in the MIX CL, which increases cholesterol synthesis and stimulates IL1B, linking effects of form of supplemental Se (TRT) on cholesterol biosynthesis and immune function in the CL.

The Role of Lipid Metabolism in Gastric Cancer

Gastric cancer has been one of the most common cancers worldwide with extensive metastasis and high mortality. Chemotherapy has been found as a main treatment for metastatic gastric cancer, whereas drug resistance limits the effectiveness of chemotherapy and leads to treatment failure. Chemotherapy resistance in gastric cancer has a complex and multifactorial mechanism, among which lipid metabolism plays a vital role. Increased synthesis of new lipids or uptake of exogenous lipids can facilitate the rapid growth of cancer cells and tumor formation. Lipids form the structural basis of biofilms while serving as signal molecules and energy sources. It is noteworthy that lipid metabolism is capable of inducing drug resistance in gastric cancer cells by reshaping the tumor micro-environment. In this study, new mechanisms of lipid metabolism in gastric cancer and the metabolic pathways correlated with chemotherapy resistance are reviewed. In particular, we discuss the effects of lipid metabolism on autophagy, biomarkers treatment and drug resistance in gastric cancer from the perspective of lipid metabolism. In brief, new insights can be gained into the development of promising therapies through an in-depth investigation of the mechanism of lipid metabolism reprogramming and resensitization to chemotherapy in gastric cancer cells, and scientific treatment can be provided by applying lipid-key enzyme inhibitors as cancer chemical sensitizers in clinical settings.

Differential cholesterol uptake in liver cells: A role for PCSK9

The clearance of low-density lipoprotein (LDL) particles from the circulation is regulated by the LDL receptor (LDLR) and proprotein convertase subtilisin/kexin 9 (PCSK9) interaction. Its disruption reduces blood cholesterol levels and delays atherosclerosis progression. Whether other members of the LDLR superfamily are in vivo targets of PCSK9 has been poorly explored. The aim of this work was to study the interaction between PCSK9 and members of the LDLR superfamily in the regulation of liver cholesterol homeostasis in an in vivo low-density lipoprotein receptor related protein 5 (LRP5) deficient mice model challenged with high-fat diet. Our results show that Wt and Lrp5^-/- mice fed a hypercholesterolemic diet (HC) have increased cholesterol ester accumulation and decreased liver LDLR and LRP5 gene and protein expression. Very low-density lipoprotein receptor (VLDLR), LRP6, LRP2, and LRP1 expression levels were analyzed in liver samples and show that they do not participate in Lrp5^-/- liver cholesterol uptake. Immunoprecipitation experiments show that LRP5 forms a complex with PCSK9 in liver-specific fat-storing stellate cells but not in structural HepG2 cells. Hepatic stellate cells silenced for LRP5 and/or PCSK9 expression and challenged with lipids show reduced cholesterol ester accumulation, indicating that both proteins are involved in lipid processing in the liver. Our results indicate that cholesterol esters accumulate in livers of Wt mice in a LDLR-family-members dependent manner as VLDLR, LRP2, and LRP6 show increased expression in HC mice. However, this increase is lost in livers of Lrp5^-/- mice, where scavenger receptors are involved in cholesterol uptake. PCSK9 expression is strongly downregulated in mice livers after HC feeding. However PCSK9 and LRP5 bind in the cytoplasm of fat storing liver cells, indicating that this PCSK9-LRP5 interaction is cell-type specific and that both proteins contribute to lipid uptake.

The Transcription Factor FgAtrR Regulates Asexual and Sexual Development, Virulence, and DON Production and Contributes to Intrinsic Resistance to Azole Fungicides in Fusarium graminearum

Simple Summary

Fusarium graminearum is a devastating plant pathogen that can cause wheat head blight. Azole fungicides are commonly used chemicals for control of this disease. However, F. graminearum strains resistant to these fungicides have emerged. To better understand the azole resistance mechanism of F. graminearum, we identified and characterized the Zn(II)2-Cys6 transcription factor FgAtrR in F. graminearum. We found that FgAtrR played critical roles in vegetative growth, conidia production, perithecium formation, and virulence on wheat heads and corn silks. FgAtrR was also involved in the resistance to azole antifungals by regulating the expression of the drug target FgCYP51s and efflux pump transporters. These results broadened our understanding of the azole resistance mechanisms of F. graminearum.

Abstract

Fusarium graminearum is the predominant causal agent of cereal Fusarium head blight disease (FHB) worldwide. The application of chemical fungicides such as azole antifungals is still the primary method for FHB control. However, to date, our knowledge of transcriptional regulation in the azole resistance of F. graminearum is quite limited. In this study, we identified and functionally characterized a Zn(II)2-Cys6 transcription factor FgAtrR in F. graminearum. We constructed a FgAtrR deletion mutant and found that deletion of FgAtrR resulted in faster radial growth with serious pigmentation defects, significantly reduced conidial production, and an inability to form perithecia. The pathogenicity of the ΔFgAtrR mutant on wheat spikes and corn silks was severely impaired with reduced deoxynivalenol production, while the tolerance to prochloraz and propiconazole of the deletion mutant was also significantly decreased. RNA-seq indicated that many metabolic pathways were affected by the deletion of FgAtrR. Importantly, FgAtrR could regulate the expression of the FgCYP51A and ABC transporters, which are the main contributors to azole resistance. These results demonstrated that FgAtrR played essential roles in asexual and sexual development, DON production, and pathogenicity, and contributed to intrinsic resistance to azole fungicides in F. graminearum. This study will help us improve the understanding of the azole resistance mechanism in F. graminearum.

Inhibition of stearoyl-CoA desaturase 1 potentiates anti-tumor activity of amodiaquine in non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is one of the leading causes of cancer related death with few therapeutic treatment options. Under adverse tumor microenvironment, autophagy is an important mechanism of metabolic adaptations to sustain the survival and proliferation of tumor cells. Therefore, targeting autophagic activity represents a promising opportunity for NSCLC treatment. Here, we found that amodiaquine (AQ) increased autophagosome numbers and LC3BII and p62 at protein levels in A549 lung cancer cells suggesting the blockade of autophagic flux by AQ. To identify the key metabolic vulnerability associated with autophagy inhibition by AQ treatment, we then performed transcriptomics analysis in the presence or absence of AQ in A549 lung cancer cells and found stearoyl-CoA desaturase 1 (SCD) 1 was one of the most highly upregulated with AQ exposure. The induction of SCD1 by AQ exposure at both protein and mRNA level suggests that SCD1 could represent a potential therapeutic target of AQ treatment. Treatment of AQ in combination with SCD1 inhibition by A939572 demonstrated robust synergistic anti-cancer efficacy in cell proliferation assay and a lung cancer mouse xenograft model. Taken together, our study identified SCD1 could be a new therapeutic target upon autophagy inhibition by AQ exposure. Combinational treatment of autophagy inhibition and SCD1 inhibition achieves synergistic anti-tumor effect both in vitro and in vivo. This combinational approach could be a promising strategy for NSCLC treatment.

A propolis-derived small molecule ameliorates metabolic syndrome in obese mice by targeting the CREB/CRTC2 transcriptional complex

The molecular targets and mechanisms of propolis ameliorating metabolic syndrome are not fully understood. Here, we report that Brazilian green propolis reduces fasting blood glucose levels in obese mice by disrupting the formation of CREB/CRTC2 transcriptional complex, a key regulator of hepatic gluconeogenesis. Using a mammalian two-hybrid system based on CREB-CRTC2, we identify artepillin C (APC) from propolis as an inhibitor of CREB-CRTC2 interaction. Without apparent toxicity, APC protects mice from high fat diet-induced obesity, decreases fasting glucose levels, enhances insulin sensitivity and reduces lipid levels in the serum and liver by suppressing CREB/CRTC2-mediated both gluconeogenic and SREBP transcriptions. To develop more potential drugs from APC, we designed and found a novel compound, A57 that exhibits higher inhibitory activity on CREB-CRTC2 association and better capability of improving insulin sensitivity in obese animals, as compared with APC. In this work, our results indicate that CREB/CRTC2 is a suitable target for developing anti-metabolic syndrome drugs.

Coordination of inter-organelle communication and lipid fluxes by OSBP-related proteins

Oxysterol-binding protein (OSBP) and OSBP-related proteins (ORPs) constitute one of the largest families of lipid-binding/transfer proteins (LTPs) in eukaryotes. The current view is that many of them mediate inter-organelle lipid transfer over membrane contact sites (MCS). The transfer occurs in several cases in a 'counter-current' fashion: A lipid such as cholesterol or phosphatidylserine (PS) is transferred against its concentration gradient driven by transport of a phosphoinositide in the opposite direction. In this way ORPs are envisioned to maintain the distinct organelle lipid compositions, with impacts on multiple organelle functions. However, the functions of ORPs extend beyond lipid homeostasis to regulation of processes such as cell survival, proliferation and migration. Important expanding areas of mammalian ORP research include their roles in viral and bacterial infections, cancers, and neuronal function. The yeast OSBP homologue (Osh) proteins execute multifaceted functions in sterol and glycerophospholipid homeostasis, post-Golgi vesicle transport, phosphatidylinositol-4-phosphate, sphingolipid and target of rapamycin (TOR) signalling, and cell cycle control. These observations identify ORPs as lipid transporters and coordinators of signals with an unforeseen variety of cellular processes. Understanding their activities not only enlightens the biology of the living cell but also allows their employment as targets of new therapeutic approaches for disease.

Turnover Rates of the Low-Density Lipoprotein Receptor and PCSK9: Added Dimension to the Cholesterol Homeostasis Model

OBJECTIVE

We measured the turnover rates of the LDLR (low-density lipoprotein receptor) and PCSK9 (proprotein convertase subtilisin/kexin type 9) in mice by metabolic labeling with heavy water and mass spectrometry. Approach and Results: In liver of mice fed high-cholesterol diets, LDLR mRNA levels and synthesis rates were markedly lower with complete suppression of cholesterol synthesis and higher cholesterol content, consistent with the Brown-Goldstein model of tissue cholesterol homeostasis. We observed markedly lower PCSK9 mRNA levels and synthesis rates in liver and lower concentrations and synthesis rates in plasma. Hepatic LDLR half-life (t½) was prolonged, consistent with an effect of reduced PCSK9, and resulted in no reduction in hepatic LDLR content despite reduced mRNA levels and LDLR synthesis rates. These changes in PCSK9 synthesis complement and expand the well-established model of tissue cholesterol homeostasis in mouse liver, in that reduced synthesis and levels of PCSK9 counterbalance lower LDLR synthesis by promoting less LDLR catabolism, thereby maintaining uptake of LDL cholesterol into liver despite high intracellular cholesterol concentrations.

CONCLUSIONS

Lower hepatic synthesis and secretion of PCSK9, an SREBP2 (sterol response element binding protein) target gene, results in longer hepatic LDLR t½ in response to cholesterol feeding in mice in the face of high intracellular cholesterol content. PCSK9 modulation opposes the canonical lowering of LDLR mRNA and synthesis by cholesterol surplus and preserves LDLR levels. The physiological and therapeutic implications of these opposing control mechanisms over liver LDLR are of interest and may reflect subservience of hepatic cholesterol homeostasis to whole body cholesterol needs.

PARPs in lipid metabolism and related diseases

PARPs and tankyrases (TNKS) represent a family of 17 proteins. PARPs and tankyrases were originally identified as DNA repair factors, nevertheless, recent advances have shed light on their role in lipid metabolism. To date, PARP1, PARP2, PARP3, tankyrases, PARP9, PARP10, PARP14 were reported to have multi-pronged connections to lipid metabolism. The activity of PARP enzymes is fine-tuned by a set of cholesterol-based compounds as oxidized cholesterol derivatives, steroid hormones or bile acids. In turn, PARPs modulate several key processes of lipid homeostasis (lipotoxicity, fatty acid and steroid biosynthesis, lipoprotein homeostasis, fatty acid oxidation, etc.). PARPs are also cofactors of lipid-responsive nuclear receptors and transcription factors through which PARPs regulate lipid metabolism and lipid homeostasis. PARP activation often represents a disruptive signal to (lipid) metabolism, and PARP-dependent changes to lipid metabolism have pathophysiological role in the development of hyperlipidemia, obesity, alcoholic and non-alcoholic fatty liver disease, type II diabetes and its complications, atherosclerosis, cardiovascular aging and skin pathologies, just to name a few. In this synopsis we will review the evidence supporting the beneficial effects of pharmacological PARP inhibitors in these diseases/pathologies and propose repurposing PARP inhibitors already available for the treatment of various malignancies.

The SREBP (Sterol Regulatory Element-Binding Protein) pathway: a regulatory bridge between carotenogenesis and sterol biosynthesis in the carotenogenic yeast Xanthophyllomyces dendrorhous

Xanthophyllomyces dendrorhous is a basidiomycete yeast that naturally produces the red–orange carotenoid astaxanthin, which has remarkable antioxidant properties. The biosynthesis of carotenoids and sterols share some common elements that have been studied in X. dendrorhous. For example, their synthesis requires metabolites derived from the mevalonate pathway and in both specific pathways, cytochrome P450 enzymes are involved that share a single cytochrome P450 reductase, CrtR, which is essential for astaxanthin biosynthesis, but is replaceable for ergosterol biosynthesis. Research on the regulation of carotenoid biosynthesis is still limited in X. dendrorhous; however, it is known that the Sterol Regulatory Element-Binding Protein (SREBP) pathway, which is a conserved regulatory pathway involved in the control of lipid metabolism, also regulates carotenoid production in X. dendrorhous. This review addresses the similarities and differences that have been observed between mammal and fungal SREBP pathways and what it is known about this pathway regarding the regulation of the production of carotenoids and sterols in X. dendrorhous.

Role of Cholesterol-Associated Steatohepatitis in the Development of NASH

The rising prevalence of nonalcoholic fatty liver disease (NAFLD) and NAFLD-related cirrhosis in the United States and globally highlights the need to better understand the mechanisms causing progression of hepatic steatosis to fibrosing steatohepatitis and cirrhosis in a small proportion of patients with NAFLD. Accumulating evidence suggests that lipotoxicity mediated by hepatic free cholesterol (FC) overload is a mechanistic driver for necroinflammation and fibrosis, characteristic of nonalcoholic steatohepatitis (NASH), in many animal models and also in some patients with NASH. Diet, lifestyle, obesity, key genetic polymorphisms, and hyperinsulinemia secondary to insulin resistance are pivotal drivers leading to aberrant cholesterol signaling, which leads to accumulation of FC within hepatocytes. FC overload in hepatocytes can lead to ER stress, mitochondrial dysfunction, development of toxic oxysterols, and cholesterol crystallization in lipid droplets, which in turn lead to hepatocyte apoptosis, necrosis, or pyroptosis. Activation of Kupffer cells and hepatic stellate cells by hepatocyte signaling and cholesterol loading contributes to this inflammation and leads to hepatic fibrosis. Cholesterol accumulation in hepatocytes can be readily prevented or reversed by statins. Observational studies suggest that use of statins in NASH not only decreases the substantially increased cardiovascular risk, but may ameliorate liver pathology. Conclusion: Hepatic FC loading may result in cholesterol-associated steatohepatitis and play an important role in the development and progression of NASH. Statins appear to provide significant benefit in preventing progression to NASH and NASH-cirrhosis. Randomized controlled trials are needed to demonstrate whether statins or statin/ezetimibe combination can effectively reverse steatohepatitis and liver fibrosis in patients with NASH.

Regulation of beta-amyloid production in neurons by astrocyte-derived cholesterol

Alzheimer's disease (AD) is characterized by the presence of amyloid β (Aβ) plaques, tau tangles, inflammation, and loss of cognitive function. Genetic variation in a cholesterol transport protein, apolipoprotein E (apoE), is the most common genetic risk factor for sporadic AD. In vitro evidence suggests that apoE links to Aβ production through nanoscale lipid compartments (lipid clusters), but its regulation in vivo is unclear. Here, we use superresolution imaging in the mouse brain to show that apoE utilizes astrocyte-derived cholesterol to specifically traffic neuronal amyloid precursor protein (APP) in and out of lipid clusters, where it interacts with β- and γ-secretases to generate Aβ-peptide. We find that the targeted deletion of astrocyte cholesterol synthesis robustly reduces amyloid and tau burden in a mouse model of AD. Treatment with cholesterol-free apoE or knockdown of cholesterol synthesis in astrocytes decreases cholesterol levels in cultured neurons and causes APP to traffic out of lipid clusters, where it interacts with α-secretase and gives rise to soluble APP-α (sAPP-α), a neuronal protective product of APP. Changes in cellular cholesterol have no effect on α-, β-, and γ-secretase trafficking, suggesting that the ratio of Aβ to sAPP-α is regulated by the trafficking of the substrate, not the enzymes. We conclude that cholesterol is kept low in neurons, which inhibits Aβ accumulation and enables the astrocyte regulation of Aβ accumulation by cholesterol signaling.