A small molecule that blocks fat synthesis by inhibiting the activation of SREBP

Phosphatidic acid directly activates mTOR and then regulates SREBP to promote ganoderic acid biosynthesis under heat stress in Ganoderma lingzhi

Ganoderic acids (GAs), a class of secondary metabolites produced by the traditional medicinal mushroom Ganoderma, are a group of triterpenoids with superior biological activities. Heat stress (HS) is one of the most important environmental abiotic stresses. Understanding how organisms sense temperature and integrate this information into their metabolism is important for determining how organisms adapt to climate change and for applying this knowledge to breeding. We previously reported that HS induced GA biosynthesis, and phospholipase D (PLD)-mediated phosphatidic acid (PA) was involved in HS-induced GA biosynthesis. We screened a proteome to identify the PA-binding proteins in G. lingzhi. We reported that PA directly interacted with mTOR and positively correlated with the ability of mTOR to promote GA biosynthesis under HS. The PA-activated mTOR pathway promoted the processing of the transcription factor sterol regulatory element-binding protein (SREBP) under HS, which directly activated GA biosynthesis. Our results suggest that SREBP is an intermediate of the PLD-mediated PA-interacting protein mTOR in HS-induced GA biosynthesis. Our report established the link between PLD-mediated PA production and the activation of mTOR and SREBP in the HS response and HS-induced secondary metabolism in filamentous fungi.

The Combined Inhibition of SREBP and mTORC1 Signaling Synergistically Inhibits B-Cell Lymphoma

BACKGROUND

The sterol regulatory element-binding protein (SREBP) pathway is essential for maintaining sterol homeostasis during B cell activation and germinal center B cell proliferation. However, its potential as a therapeutic target to treat B-cell lymphoma remains unclear.

METHODS

We examined SREBP protein expression in human B-cell lymphoma samples using immunohistochemistry. Additionally, we conducted in vitro studies using SREBP signaling inhibitors in combination with rapamycin to assess their effects on cell proliferation and lipid metabolism in B-cell lymphoma cells.

RESULTS

Our analysis revealed high levels of SREBP2 protein expression in human B-cell lymphoma samples. Inhibiting SREBP signaling or its downstream target HMG-CoA reductase (HMGCR) with Fatostatin or Simvastatin effectively suppressed B-cell lymphoma cell proliferation. However, B-cell lymphoma cells responded to statin treatment by activating the mTORC1-pS6 pathway, suggesting a compensatory mechanism to overcome statin-induced cell cycle arrest. Combining low-dose statin treatment with the mTOR inhibitor rapamycin produced a synergistic effect, significantly inhibiting B-cell lymphoma proliferation, cell cycle progression, and lipid raft formation.

CONCLUSIONS

These results highlight the potential of a combined therapeutic approach targeting both SREBP and mTORC1 as a novel strategy for treating B-cell lymphoma.

Srebp-1 bridges gonad development and lipid accumulation by regulating lipogenesis in noble scallop Chlamys nobilis

In bivalve, development of female gonad is accompanied with accumulating lipids which provided energy resource for non-feeding larvae development. As the major transcriptional regulators of lipid metabolism, Srebps play pivotal role in lipid homeostasis during oogenesis. However, little work was conducted on Srebps function in bivalves. The noble scallop Chlamys nobilis accumulated large amount of lipids in its gonad during oogenesis. Here, we identified a single Srebp gene (named Srebp-1) with a high similarity to human Srebp-1c. Disrupting Srebp-1 with Betulin (inhibiting the maturation of Srebp protein) repressed expression of lipogenic genes and de novo lipogenesis, and resulted in reduction of gonad index and lipid deposition, suggesting a crucial role of Srebp-1 for gonad development and lipid synthesis in female gonad. Additionally, scallops with Srebp-1 disruption released fewer eggs with a reduction in their lipid content and D-larvae formation, revealing an impair of fecundity caused by Srebp-1 disruption. Cold exposure stimulated lipid accumulation which required Srebp-1 to regulate de novo lipogenesis and lipid uptake, providing a crosstalk of Srebp-1 activity and environmental variation on lipid accumulation in noble scallop. Thus, our study identified Srebp-1 as a central regulator coordinating the lipid synthesis and accumulation with gonad development in noble scallop.

Exploring the glycation association with dyslipidaemia: Novel approach for diabetic nephropathy

The transcription factor known as sterol regulatory element-binding protein (SREBP) and the glycation pathways, specifically the formation of Advanced Glycation End Products (AGEs), have a significant and deleterious impact on the kidney. They alter renal lipid metabolism and promote glomerulosclerosis, mesangial cell expansion, tubulointerstitial fibrosis, and inflammation, leading to diabetic nephropathy (DN) progression. Although several pieces of scientific evidence are reported for potential causes of glycation and lipotoxicity in DN, the underlying mechanism of renal lipid accumulation still needs to be fully understood. We provide a rationalized view on how AGEs exert multiple effects that cause SREBP activation and inflammation, contributing to DN through Receptor for AGEs (RAGE) signaling, AGE-R1-dependent downregulation of Sirtuin 1 (SIRT-1), and increased SREBP Cleavage Activating Protein (SCAP) glycosylation. This review emphasizes the association between glycation and the SREBP pathway and how it affects the onset of DN associated with obesity. Finally, we discuss the correlation of glycation and the SREBP pathway with insulin resistance (IR), oxidative stress, endoplasmic reticulum stress, inflammation, and existing and emerging therapeutic approaches toward better controlling obesity-related DN.

The potential role of transcription factor sterol regulatory element binding proteins (SREBPs) in Alzheimer's disease

Sterol regulatory element binding proteins (SREBPs) are a series of cholesterol-related transcription factors. Their role in regulating brain cholesterol biosynthesis, amyloid accumulation, and tau tangles formation has been intensively studied in protein-protein interaction analysis based on genes in clinical databases. SREBPs play an important role in maintaining cholesterol homeostasis in the brain. There are three subtypes of SREBPs, SREBP-1a stimulates the expression of genes related to cholesterol and fatty acid synthesis, SREBP-1c stimulates adipogenesis, and SREBP-2 stimulates cholesterol synthase and LDL receptors. SREBP-2 is activated in response to cholesterol depletion and stimulates a compensatory upregulation of cholesterol uptake and synthesis. Previous studies have shown that inhibition of SREBP-2 reduces cholesterol and amyloid accumulation, and new research suggests that SREBPs play a multifaceted role in Alzheimer's disease. Here, we highlight the importance of SREBPs in AD, in terms of multiple pathways regulating cholesterol in the brain, and primarily demonstrate the potential of SREBP-2 inhibitors. There was a trend towards a significant increase in the expression levels of different SREBP isoforms in AD patients compared to healthy controls. Therefore, there is a close link between SREBPs and AD, and this review analyses the potential role of SREBPs in the treatment of AD. In addition, we systematically reviewed the research progress of SREBPs in AD, and this review will provide more innovative insights into the pathogenesis and treatment of AD and new strategies for drug development in AD.

Mutant p53 regulates cancer cell invasion in complex three-dimensional environments through mevalonate pathway-dependent Rho/ROCK signaling

Certain mutations can confer neomorphic gain of function (GOF) activities to the p53 protein that affect cancer progression. Yet the concept of mutant p53 GOF has been challenged. Here, using various strategies to alter the status of mutant versions of p53 in different cell lines, we demonstrate that mutant p53 stimulates cancer cell invasion in three-dimensional environments. Mechanistically, mutant p53 enhances RhoA/ROCK-dependent cell contractility and cell-mediated extracellular matrix (ECM) re-organization via increasing mevalonate pathway-dependent RhoA localization to the membrane. In line with this, RhoA-dependent pro-invasive activity is also mediated by IDI-1, a mevalonate pathway product. Further, the invasion-enhancing effect of mutant p53 is dictated by the biomechanical properties of the surrounding ECM, thereby adding a cell-independent layer of regulation to mutant p53 GOF activity that is mediated by dynamic reciprocal cell-ECM interactions. Together our findings link mutant p53 metabolic GOF activity with an invasive cellular phenotype in physiologically relevant and context-dependent settings.

Significance

This study addresses the contribution of mutant p53 to the process of cancer cell dissemination in physiologically relevant three-dimensional environments - a key characteristic of metastatic disease. Several mutant p53 proteins display pro-oncogenic activity with respect to cancer cell invasion in 3D environments via mevalonate pathway-dependent Rho/ROCK signaling axis.

Discovery of N-Aryl-N'-[4-(aryloxy)cyclohexyl]squaramide-Based Inhibitors of LXR/SREBP-1c Signaling Pathway Ameliorating Steatotic Liver Disease: Navigating the Role of SIRT6 Activation

Metabolic dysfunction-associated steatotic liver disease (MASLD) is primarily attributed to the abnormal upregulation of hepatic lipogenesis, which is especially caused by the overactivation of the liver X receptor/sterol regulatory element-binding protein-1c (LXR/SREBP-1c) pathway in hepatocytes. In this study, we report the rational design and synthesis of a novel series of squaramides via bioisosteric replacement, which was evaluated for its inhibitory activity on the LXR/SREBP-1c pathway using dual cell-based assays. Compound 31 was found to significantly downregulate LXR, SREBP-1c, and their target genes associated with lipogenesis. Further investigation revealed that compound 31 may indirectly inhibit the LXR/SREBP-1c pathway by activating the upstream regulator sirtuin 6 (SIRT6). Encouragingly, compound 31 substantially attenuated lipid accumulation in HepG2 cells and in the liver of high-fat-diet-fed mice. These findings suggest that compound 31 holds promise as a candidate for the development of treatments for MASLD and other lipid metabolism-related diseases.

Serum apolipoprotein H determines ferroptosis resistance by modulating cellular lipid composition

Ferroptosis is a regulated cell death process dependent on iron, triggered by the accumulation of lipid peroxidation. The environmental context significantly impacts cellular sensitivities to ferroptosis. Serum, constituting the extracellular fluid composition in vivo, provides crucial environmental biomolecules. In this study, we investigated the influence of sera on ferroptosis induction, pinpointing the serum protein apolipoprotein H (APOH) as a pivotal inhibitor of ferroptosis. Moreover, we elucidated that APOH suppresses ferroptosis by activating the phosphoinositide 3-kinase (PI3K)-AKT-sterol regulatory element-binding proteins (SREBPs) pathway, thereby elevating stearoyl-CoA desaturase (SCD) levels and augmenting cellular monounsaturated fatty acid-containing phospholipids (MUFA-PLs). Furthermore, ApoHinfer, the peptide derivative of the active region of APOH, mimics its ferroptosis inhibitory activity. Our findings underscore the critical role of serum protein APOH in the inhibition of ferroptosis and indicates potential therapeutic applications in treating cancer and diseases associated with ferroptosis.

Role of low-density cholesterol and Interleukin-17 interaction in breast cancer pathogenesis and treatment

Breast cancer (BC) has become the most prevalent cancer worldwide, and further research is being conducted to deepen our understanding of its pathogenesis and treatment. Lipid metabolism disorder is a significant alteration in cancer cells, and the investigation into the role of Interleukin-17 (IL-17) in malignant tumors has emerged as a research focus in recent years. Thus, exploring changes in lipid metabolism and inflammatory factors in BC cells is crucial in identifying potential therapeutic targets. This article summarizes the progress made in the research on the main low-density cholesterol (LDL) transporter and IL-17 in lipid metabolism, and their potential involvement in the development of BC. The article aims to establish a theoretical foundation for the development of BC-related therapies.

Regulation of cholesterol biosynthesis by CTCF and H3K27 methylation is critical for cell migration

CTCF is a key factor in three-dimensional chromatin folding and transcriptional control that was found to affect cancer cell migration by a mechanism that is still poorly understood. To identify this mechanism, we used mouse melanoma cells with a partial loss of function (pLoF) of CTCF. We found that CTCF pLoF inhibits cell migration rate while leading to an increase in the expression of multiple enzymes in the cholesterol biosynthesis pathway along with an elevation in the cellular cholesterol level. In agreement with the cholesterol change we detected altered membrane dynamics in CTCF pLoF cells as measured by reduced formation of migrasomes, extracellular vesicles formed at the rear side of migrating cells. Inhibition of cholesterol synthesis in CTCF pLoF cells restored the cellular migration rate and migrasome formation, suggesting that CTCF supports cell migration by suppressing cholesterol synthesis. Detailed analysis of the promoter of Hmgcs1, an early enzyme in the cholesterol synthesis pathway, revealed that CTCF prevents formation of a loop between that promoter and another promoter 200 kb away. CTCF also supports PRC2 recruitment to the promoter and deposition of H3K27me3. H3K27me3 at the promoter of Hmgcs1 prevents SREBP2 binding and activation of transcription. By this mechanism, CTCF fine-tunes cholesterol levels to support cell migration. Notably, genome wide association studies suggest a link between CTCF and cholesterol-associated diseases, thus CTCF emerges as a new regulator of cholesterol biosynthesis.

The SARIFA biomarker in the context of basic research of lipid-driven cancers

SARIFA was very recently introduced as a histomorphological biomarker with strong prognostic power for colorectal, gastric, prostate, and pancreatic cancer. It is characterized by the direct contact between tumor cells and adipocytes due to a lack of stromal reaction. This can be easily evaluated on routinely available H&E-slides with high interobserver agreement. SARIFA also reflects a specific tumor biology driven by metabolic reprogramming. Tumor cells in SARIFA-positive tumors benefit from direct interaction with adipocytes as an external source of lipids. Numerous studies have shown that lipid metabolism is crucial in carcinogenesis and cancer progression. We found that the interaction between tumor cells and adipocytes was not triggered by obesity, as previously assumed. Instead, we believe that this is due to an immunological mechanism. Knowledge about lipid metabolism in cancer from basic experiments can be transferred to develop strategies targeting this reprogramed metabolism.

Insulin receptor isoform B is required for efficient proinsulin processing in pancreatic β cells

The insulin receptor (INSR, IR) has two isoforms, IRA and IRB, through alternative splicing. However, their distinct functions in vivo remain unclear. Here we generated β cell-specific IRB knockout (KO) mice (βIRBKO). The KO mice displayed worsened hyperinsulinemia and hyperproinsulinemia in diet-induced obesity due to impaired proinsulin processing in β cells. Mechanistically, loss of IRB suppresses eukaryotic translation initiation factor 4G1 (eIF4G1) by stabilizing the transcriptional receptor sterol-regulatory element binding protein 1 (SREBP1). Moreover, excessive autocrine proinsulin in βIRBKO mice enhances the activity of extracellular signal-regulated kinase (ERK) through the remaining IRA to further stabilize nuclear SREBP1, forming a feedback loop. Collectively, our study paves the way to dissecting the isoform-specific function of IR in vivo and highlights the important roles of IRB in insulin processing and protecting β cells from lipotoxicity in obesity.

Human cytomegalovirus infection impairs neural differentiation via repressing sterol regulatory element binding protein 2-mediated cholesterol biosynthesis

Congenital human cytomegalovirus (HCMV) infection is a major cause of abnormalities and disorders in the central nervous system (CNS) and/or the peripheral nervous system (PNS). However, the complete pathogenesis of neural differentiation disorders caused by HCMV infection remains to be fully elucidated. Stem cells from human exfoliated deciduous teeth (SHEDs) are mesenchymal stem cells (MSCs) with a high proliferation and neurogenic differentiation capacity. Since SHEDs originate from the neural crest of the early embryonic ectoderm, SHEDs were hypothesized to serve as a promising cell line for investigating the pathogenesis of neural differentiation disorders in the PNS caused by congenital HCMV infection. In this work, SHEDs were demonstrated to be fully permissive to HCMV infection and the virus was able to complete its life cycle in SHEDs. Under neurogenic inductive conditions, HCMV infection of SHEDs caused an abnormal neural morphology. The expression of stem/neural cell markers was also disturbed by HCMV infection. The impairment of neural differentiation was mainly due to a reduction of intracellular cholesterol levels caused by HCMV infection. Sterol regulatory element binding protein-2 (SREBP2) is a critical transcription regulator that guides cholesterol synthesis. HCMV infection was shown to hinder the migration of SREBP2 into nucleus and resulted in perinuclear aggregations of SREBP2 during neural differentiation. Our findings provide new insights into the prevention and treatment of nervous system diseases caused by congenital HCMV infection.

Regulation and targeting of SREBP-1 in hepatocellular carcinoma

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

STAT3 activation of SCAP-SREBP-1 signaling upregulates fatty acid synthesis to promote tumor growth

SCAP plays a central role in controlling lipid homeostasis by activating SREBP-1, a master transcription factor in controlling fatty acid (FA) synthesis. However, how SCAP expression is regulated in human cancer cells remains unknown. Here, we revealed that STAT3 binds to the promoter of SCAP to activate its expression across multiple cancer cell types. Moreover, we identified that STAT3 also concurrently interacts with the promoter of SREBF1 gene (encoding SREBP-1), amplifying its expression. This dual action by STAT3 collaboratively heightens FA synthesis. Pharmacological inhibition of STAT3 significantly reduces the levels of unsaturated FAs and phospholipids bearing unsaturated FA chains by reducing the SCAP-SREBP-1 signaling axis and its downstream effector SCD1. Examination of clinical samples from patients with glioblastoma, the most lethal brain tumor, demonstrates a substantial co-expression of STAT3, SCAP, SREBP-1, and SCD1. These findings unveil STAT3 directly regulates the expression of SCAP and SREBP-1 to promote FA synthesis, ultimately fueling tumor progression.

Sequential drug treatment targeting cell cycle and cell fate regulatory programs blocks non-genetic cancer evolution in acute lymphoblastic leukemia

BACKGROUND

Targeted therapies exploiting vulnerabilities of cancer cells hold promise for improving patient outcome and reducing side-effects of chemotherapy. However, efficacy of precision therapies is limited in part because of tumor cell heterogeneity. A better mechanistic understanding of how drug effect is linked to cancer cell state diversity is crucial for identifying effective combination therapies that can prevent disease recurrence.

RESULTS

Here, we characterize the effect of G2/M checkpoint inhibition in acute lymphoblastic leukemia (ALL) and demonstrate that WEE1 targeted therapy impinges on cell fate decision regulatory circuits. We find the highest inhibition of recovery of proliferation in ALL cells with KMT2A-rearrangements. Single-cell RNA-seq and ATAC-seq of RS4;11 cells harboring KMT2A::AFF1, treated with the WEE1 inhibitor AZD1775, reveal diversification of cell states, with a fraction of cells exhibiting strong activation of p53-driven processes linked to apoptosis and senescence, and disruption of a core KMT2A-RUNX1-MYC regulatory network. In this cell state diversification induced by WEE1 inhibition, a subpopulation transitions to a drug tolerant cell state characterized by activation of transcription factors regulating pre-B cell fate, lipid metabolism, and pre-BCR signaling in a reversible manner. Sequential treatment with BCR-signaling inhibitors dasatinib, ibrutinib, or perturbing metabolism by fatostatin or AZD2014 effectively counteracts drug tolerance by inducing cell death and repressing stemness markers.

CONCLUSIONS

Collectively, our findings provide new insights into the tight connectivity of gene regulatory programs associated with cell cycle and cell fate regulation, and a rationale for sequential administration of WEE1 inhibitors with low toxicity inhibitors of pre-BCR signaling or metabolism.

Elucidating the Role of Lipid-Metabolism-Related Signal Transduction and Inhibitors in Skin Cancer

Lipids, as multifunctional molecules, play a crucial role in a variety of cellular processes. These include regulating membrane glycoprotein functions, controlling membrane trafficking, influencing apoptotic pathways, and affecting drug transport. In addition, lipid metabolites can alter the surrounding microenvironment in ways that might encourage tumor progression. The reprogramming of lipid metabolism is pivotal in promoting tumorigenesis and cancer progression, with tumors often displaying significant changes in lipid profiles. This review concentrates on the essential factors that drive lipid metabolic reprogramming, which contributes to the advancement and drug resistance in melanoma. Moreover, we discuss recent advances and current therapeutic strategies that employ small-molecule inhibitors to target lipid metabolism in skin cancers, particularly those associated with inflammation and melanoma.

Fatostatin promotes anti-tumor immunity by reducing SREBP2 mediated cholesterol metabolism in tumor-infiltrating T lymphocytes

Aberrant lipid metabolism impacts intratumoral T cell-mediated immune response and tumor growth. Fatostatin functions as an inhibitor of sterol regulatory element binding protein (SREBP) activation. However, the complex effects of fatostatin on cholesterol metabolism in the tumor microenvironment (TME) and its influence on T cell anti-tumor immunity remain unclear. In this study, fatostatin effectively suppressed B16 melanoma, MC38 colon cancer, and Lewis lung cancer (LLC) transplanted tumor growth in immunocompetent mice by reducing SREBPs-mediated lipid metabolism, especially cholesterol levels. Mechanistically, fatostatin decreased intracellular cholesterol accumulation and inhibited X-box binding protein 1 (XBP1)-mediated endoplasmic reticulum (ER) stress, reducing Treg cells and alleviating CD8+ T cell exhaustion in the TME, exerting anti-tumor activity. Nevertheless， this effect was impaired in immunodeficient nude mice, suggesting fatostatin's anti-tumor efficacy in transplanted tumors partly relies on T cell-mediated anti-tumor immunity. Our study highlights SREBP2-mediated cholesterol metabolism as a potential strategy for anti-tumor immunotherapy, and confirms fatostatin's promise in tumor immunotherapy.

Discovery of Novel Binders to Sterol Regulatory Element-Binding Protein-1 by High-Throughput Screening

Sterol regulatory element-binding protein-1 (SREBP-1) is a transcription factor that regulates the expression of genes related to fatty acid biosynthesis. Its high expression and activation in obesity and associated metabolic diseases make it a potential therapeutic target. However, the role of SREBP-1 in the development and exacerbation of these diseases remains unclear, partly because of the impossibility of inhibiting its function because of the lack of specific inhibitors. Here, we aimed to identify small-molecule compounds that directly bind to SREBP-1 using the recombinant N-terminal region of SREBP-1a, which is required for its transcriptional activity. A high-throughput screening campaign was conducted using a thermal shift assay and surface plasmon resonance assay to evaluate the compound affinity and specificity, which resulted in the identification of two compounds. Future analysis of their structure-activity relationships may lead to the development of specific SREBP-1 inhibitors, thereby potentially validating SREBP-1 as a therapeutic target for obesity and resultant atherosclerotic diseases.

Cytotoxic sigma-2 ligands trigger cancer cell death via cholesterol-induced-ER-stress

Sigma-2-ligands (S2L) are characterized by high binding affinities to their cognate sigma-2 receptor, overexpressed in rapidly proliferating tumor cells. As such, S2L were developed as imaging probes (ISO1) or as cancer therapeutics, alone (SV119 [C6], SW43 [C10]) and as delivery vehicles for cytotoxic drug cargoes (C6-Erastin, C10-SMAC). However, the exact mechanism of S2L-induced cytotoxicity remains to be fully elucidated. A series of high-affinity S2L were evaluated regarding their cytotoxicity profiles across cancer cell lines. While C6 and C10 displayed distinct cytotoxicities, C0 and ISO1 were essentially non-toxic. Confocal microscopy and lipidomics analysis in cellular and mouse models revealed that C10 induced increases in intralysosomal free cholesterol and in cholesterol esters, suggestive of unaltered intracellular cholesterol trafficking. Cytotoxicity was caused by cholesterol excess, a phenomenon that contrasts the effects of NPC1 inhibition. RNA-sequencing revealed gene clusters involved in cholesterol homeostasis and ER stress response exclusively by cytotoxic S2L. ER stress markers were confirmed by qPCR and their targeted modulation inhibited or enhanced cytotoxicity of C10 in a predicted manner. Moreover, C10 increased sterol regulatory element-binding protein 2 (SREBP2) and low-density lipoprotein receptor (LDLR), both found to be pro-survival factors activated by ER stress. Furthermore, inhibition of downstream processes of the adaptive response to S2L with simvastatin resulted in synergistic treatment outcomes in combination with C10. Of note, the S2L conjugates retained the ER stress response of the parental ligands, indicative of cholesterol homeostasis being involved in the overall cytotoxicity of the drug conjugates. Based on these findings, we conclude that S2L-mediated cell death is due to free cholesterol accumulation that leads to ER stress. Consequently, the cytotoxic profiles of S2L drug conjugates are proposed to be enhanced via concurrent ER stress inducers or simvastatin, strategies that could be instrumental on the path toward tumor eradication.

A cholesterol-binding bacterial toxin provides a strategy for identifying a specific Scap inhibitor that blocks lipid synthesis in animal cells

Lipid synthesis is regulated by the actions of Scap, a polytopic membrane protein that binds cholesterol in membranes of the endoplasmic reticulum (ER). When ER cholesterol levels are low, Scap activates SREBPs, transcription factors that upregulate genes for synthesis of cholesterol, fatty acids, and triglycerides. When ER cholesterol levels rise, the sterol binds to Scap, triggering conformational changes that prevent activation of SREBPs and halting synthesis of lipids. To achieve a molecular understanding of how cholesterol regulates the Scap/SREBP machine and to identify therapeutics for dysregulated lipid metabolism, cholesterol-mimetic compounds that specifically bind and inhibit Scap are needed. To accomplish this goal, we focused on Anthrolysin O (ALO), a pore-forming bacterial toxin that binds cholesterol with a specificity and sensitivity that is uncannily similar to Scap. We reasoned that a small molecule that would bind and inhibit ALO might also inhibit Scap. High-throughput screening of a ~300,000-compound library for ALO-binding unearthed one molecule, termed UT-59, which binds to Scap's cholesterol-binding site. Upon binding, UT-59 triggers the same conformation changes in Scap as those induced by cholesterol and blocks activation of SREBPs and lipogenesis in cultured cells. UT-59 also inhibits SREBP activation in the mouse liver. Unlike five previously reported inhibitors of SREBP activation, UT-59 is the only one that acts specifically by binding to Scap's cholesterol-binding site. Our approach to identify specific Scap inhibitors such as UT-59 holds great promise in developing therapeutic leads for human diseases stemming from elevated SREBP activation, such as fatty liver and certain cancers.

BHLHE40 Inhibits Ferroptosis in Pancreatic Cancer Cells via Upregulating SREBF1

Pancreatic cancer (PCa) is one of the most fatal human malignancies. The enhanced infiltration of stromal tissue into the PCa tumor microenvironment limits the identification of key tumor-specific transcription factors and epigenomic abnormalities in malignant epithelial cells. Integrated transcriptome and epigenetic multiomics analyses of the paired PCa organoids indicate that the basic helix-loop-helix transcription factor 40 (BHLHE40) is significantly upregulated in tumor samples. Increased chromatin accessibility at the promoter region and enhanced mTOR pathway activity contribute to the elevated expression of BHLHE40. Integrated analysis of chromatin immunoprecipitation-seq, RNA-seq, and high-throughput chromosome conformation capture data, together with chromosome conformation capture assays, indicate that BHLHE40 not only regulates sterol regulatory element-binding factor 1 (SREBF1) transcription as a classic transcription factor but also links the enhancer and promoter regions of SREBF1. It is found that the BHLHE40-SREBF1-stearoyl-CoA desaturase axis protects PCa cells from ferroptosis, resulting in the reduced accumulation of lipid peroxidation. Moreover, fatostatin, an SREBF1 inhibitor, significantly suppresses the growth of PCa tumors with high expressions of BHLHE40. This study highlights the important roles of BHLHE40-mediated lipid peroxidation in inducing ferroptosis in PCa cells and provides a novel mechanism underlying SREBF1 overexpression in PCa.

Corydalis saxicola Bunting total alkaloids improve NAFLD by suppressing de novo lipogenesis through the AMPK-SREBP1 axis

ETHNOPHARMACOLOGICAL RELEVANCE

Along with the gradually increasing incidence, nonalcoholic fatty liver disease (NAFLD) has already been influencing the health of more and more people in the world. Corydalis saxicola Bunting (CSB), a valuable folk medicine, is the dried whole grass of a perennial herb, Yanhuanglian (Papaveraceae), which has significant effects on various hepatitis, liver fibrosis, cirrhosis and other liver diseases. Corydalis saxicola Bunting total alkaloids (CSBTA), a mixture of alkaloids extracted from CSB, exhibit widely-accepted hepatoprotective effects.

AIM OF THE STUDY

This study aimed to explore the therapeutic potential of CSBTA on NAFLD and the underlying mechanism.

MATERIALS AND METHODS

A mice model was established by high fat and high cholesterol diet (HFHCD) to study the benefits of CSBTA on the progression of NAFLD. The efficacy of CSBTA on NAFLD was revealed systematically via RNA-sequencing analysis. Further efficacy and molecular mechanism study were explored in mouse primary hepatocytes and HepG2 cells stimulated with high energy with or without pharmacological inhibition or gene silencing.

RESULTS

CSBTA effectively improved the major hallmarks of NAFLD including liver lipid accumulation, liver injury, inflammation and fibrosis in HFHCD-fed mice. RNA sequencing and targeted qPCR analysis jointly evidenced CSBTA significantly suppressed the expression of Srebf1, Acc1 and Fasn which are the genes responsible for fatty acid biosynthesis. Moreover, stable isotope tracer test denoted CSBTA reduced lipid accumulation via interrupting fatty acid biosynthesis in hepatocytes or the liver. Mechanistically, CSBTA could impede SREBP1 maturation via AMPK activation, thereby reducing DNL-derived lipid accumulation in hepatocytes.

CONCLUSIONS

CSBTA protected against hepatic steatosis and other hallmarks of NAFLD induced by HFHCD via suppressing DNL, through modulating the AMPK-SREBP1 axis. CSBTA may therefore have a therapeutic potential for NAFLD treatment.

Pseudorabies virus upregulates low-density lipoprotein receptors to facilitate viral entry

Pseudorabies virus (PRV) is the causative agent of Aujeszky's disease in pigs. The low-density lipoprotein receptor (LDLR) is a transcriptional target of the sterol-regulatory element-binding proteins (SREBPs) and participates in the uptake of LDL-derived cholesterol. However, the involvement of LDLR in PRV infection has not been well characterized. We observed an increased expression level of LDLR mRNA in PRV-infected 3D4/21, PK-15, HeLa, RAW264.7, and L929 cells. The LDLR protein level was also upregulated by PRV infection in PK-15 cells and in murine lung and brain. The treatment of cells with the SREBP inhibitor, fatostatin, or with SREBP2-specific small interfering RNA prevented the PRV-induced upregulation of LDLR expression as well as viral protein expression and progeny virus production. This suggested that PRV activated SREBPs to induce LDLR expression. Furthermore, interference in LDLR expression affected PRV proliferation, while LDLR overexpression promoted it. This indicated that LDLR was involved in PRV infection. The study also demonstrated that LDLR participated in PRV invasions. The overexpression of LDLR or inhibition of proprotein convertase subtilisin/kexin type 9 (PCSK9), which binds to LDLR and targets it for lysosomal degradation, significantly enhanced PRV attachment and entry. Mechanistically, LDLR interacted with PRV on the plasma membrane, and pretreatment of cells with LDLR antibodies was able to neutralize viral entry. An in vivo study indicated that the treatment of mice with the PCSK9 inhibitor SBC-115076 promoted PRV proliferation. The data from the study indicate that PRV hijacks LDLR for viral entry through the activation of SREBPs.IMPORTANCEPseudorabies virus (PRV) is a herpesvirus that primarily manifests as fever, pruritus, and encephalomyelitis in various domestic and wild animals. Owing to its lifelong latent infection characteristics, PRV outbreaks have led to significant financial setbacks in the global pig industry. There is evidence that PRV variant strains can infect humans, thereby crossing the species barrier. Therefore, gaining deeper insights into PRV pathogenesis and developing updated strategies to contain its spread are critical. This study posits that the low-density lipoprotein receptor (LDLR) could be a co-receptor for PRV infection. Hence, strategies targeting LDLR may provide a promising avenue for the development of effective PRV vaccines and therapeutic interventions.

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.

SREBPs as the potential target for solving the polypharmacy dilemma

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

The RORɣ/SREBP2 pathway is a master regulator of cholesterol metabolism and serves as potential therapeutic target in t(4;11) leukemia

Dysregulated cholesterol homeostasis promotes tumorigenesis and progression. Therefore, metabolic reprogramming constitutes a new hallmark of cancer. However, until today, only few therapeutic approaches exist to target this pathway due to the often-observed negative feedback induced by agents like statins leading to controversially increased cholesterol synthesis upon inhibition. Sterol regulatory element-binding proteins (SREBPs) are key transcription factors regulating the synthesis of cholesterol and fatty acids. Since SREBP2 is difficult to target, we performed pharmacological inhibition of retinoic acid receptor (RAR)-related orphan receptor gamma (RORγ), which acts upstream of SREBP2 and serves as master regulator of the cholesterol metabolism. This resulted in an inactivated cholesterol-related gene program with significant downregulation of cholesterol biosynthesis. Strikingly, these effects were more pronounced than the effects of fatostatin, a direct SREBP2 inhibitor. Upon RORγ inhibition, RNA sequencing showed strongly increased cholesterol efflux genes leading to leukemic cell death and cell cycle changes in a dose- and time-dependent manner. Combinatorial treatment of t(4;11) cells with the RORγ inhibitor showed additive effects with cytarabine and even strong anti-leukemia synergism with atorvastatin by circumventing the statin-induced feedback. Our results suggest a novel therapeutic strategy to inhibit tumor-specific cholesterol metabolism for the treatment of t(4;11) leukemia.

Targeting metabolic reprogramming in hepatocellular carcinoma to overcome therapeutic resistance: A comprehensive review

Hepatocellular carcinoma (HCC) poses a heavy burden on human health with high morbidity and mortality rates. Systematic therapy is crucial for advanced and mid-term HCC, but faces a significant challenge from therapeutic resistance, weakening drug effectiveness. Metabolic reprogramming has gained attention as a key contributor to therapeutic resistance. Cells change their metabolism to meet energy demands, adapt to growth needs, or resist environmental pressures. Understanding key enzyme expression patterns and metabolic pathway interactions is vital to comprehend HCC occurrence, development, and treatment resistance. Exploring metabolic enzyme reprogramming and pathways is essential to identify breakthrough points for HCC treatment. Targeting metabolic enzymes with inhibitors is key to addressing these points. Inhibitors, combined with systemic therapeutic drugs, can alleviate resistance, prolong overall survival for advanced HCC, and offer mid-term HCC patients a chance for radical resection. Advances in metabolic research methods, from genomics to metabolomics and cells to organoids, help build the HCC metabolic reprogramming network. Recent progress in biomaterials and nanotechnology impacts drug targeting and effectiveness, providing new solutions for systemic therapeutic drug resistance. This review focuses on metabolic enzyme changes, pathway interactions, enzyme inhibitors, research methods, and drug delivery targeting metabolic reprogramming, offering valuable references for metabolic approaches to HCC treatment.

Enhanced SREBP2-driven cholesterol biosynthesis by PKCλ/ι deficiency in intestinal epithelial cells promotes aggressive serrated tumorigenesis

The metabolic and signaling pathways regulating aggressive mesenchymal colorectal cancer (CRC) initiation and progression through the serrated route are largely unknown. Although relatively well characterized as BRAF mutant cancers, their poor response to current targeted therapy, difficult preneoplastic detection, and challenging endoscopic resection make the identification of their metabolic requirements a priority. Here, we demonstrate that the phosphorylation of SCAP by the atypical PKC (aPKC), PKCλ/ι promotes its degradation and inhibits the processing and activation of SREBP2, the master regulator of cholesterol biosynthesis. We show that the upregulation of SREBP2 and cholesterol by reduced aPKC levels is essential for controlling metaplasia and generating the most aggressive cell subpopulation in serrated tumors in mice and humans. Since these alterations are also detected prior to neoplastic transformation, together with the sensitivity of these tumors to cholesterol metabolism inhibitors, our data indicate that targeting cholesterol biosynthesis is a potential mechanism for serrated chemoprevention.

Targeting dysregulated lipid metabolism in the tumor microenvironment

The reprogramming of lipid metabolism and its association with oncogenic signaling pathways within the tumor microenvironment (TME) have emerged as significant hallmarks of cancer. Lipid metabolism is defined as a complex set of molecular processes including lipid uptake, synthesis, transport, and degradation. The dysregulation of lipid metabolism is affected by enzymes and signaling molecules directly or indirectly involved in the lipid metabolic process. Regulation of lipid metabolizing enzymes has been shown to modulate cancer development and to avoid resistance to anticancer drugs in tumors and the TME. Because of this, understanding the metabolic reprogramming associated with oncogenic progression is important to develop strategies for cancer treatment. Recent advances provide insight into fundamental mechanisms and the connections between altered lipid metabolism and tumorigenesis. In this review, we explore alterations to lipid metabolism and the pivotal factors driving lipid metabolic reprogramming, which exacerbate cancer progression. We also shed light on the latest insights and current therapeutic approaches based on small molecular inhibitors and phytochemicals targeting lipid metabolism for cancer treatment. Further investigations are worthwhile to fully understand the underlying mechanisms and the correlation between altered lipid metabolism and carcinogenesis.

Recent advancements in nanomedicine based lipid metabolism for tumour immunotherapy

Therapy on lipid metabolism is emerging as a groundbreaking cancer treatment, offering the unprecedented opportunity to effectively treat and in several cases. Tumorigenesis is inextricably linked to lipid metabolism. In this regard, the features of lipid metabolism include lipid synthesis, decomposition, metabolism and lipid storage and mobilisation from intracellular lipid droplets. Most importantly, the regulation of lipid metabolism is central to the appropriate immune response of tumour cells, and ultimately to exert the immune efforts to realise the perspective of many anti-tumour effects. Different cancers and immune cells have different dependence on lipid metabolism, playing a pivotal role in differentiation and function of immune cells. However, what lies before the immunotherapy targeting lipid metabolism is side effects of systemic toxicity and defects of individual drugs, which strongly highlights that nanodelivery strategy is a magnet for it to enhance drug efficiency, reduce drug toxicity and improve application deficiencies. This review will first focus on emerging research progress of lipid metabolic reprogramming mechanism, and then explore the complex role of lipid metabolism in the tumour cells including the effect on immune cells and their nano-preparations of monotherapy and multiple therapies used in combination, in a shift away from conventional cancer research.HighlightsThe regulation of lipid metabolism is central to the appropriate immune response of tumour cells, and ultimately to exert the immune efforts to realise the perspective of many anti-tumour effects.Preparations of focusing lipid metabolism have side effects of systemic toxicity and defects of individual drugs. It strongly highlights that nanodelivery strategy is a magnet for it to enhance drug efficiency, reduce drug toxicity and improve application deficiencies.This review will first focus on emerging research progress of lipid metabolic reprogramming mechanism, and then explore the complex role of lipid metabolism in the tumour cells including the effect on immune cells as well as their nano-preparations of monotherapy and multiple therapies used in combination, in a shift away from conventional cancer research.

Metabolic reprogramming and its clinical implication for liver cancer

Cancer cells often encounter hypoxic and hypo-nutrient conditions, which force them to make adaptive changes to meet their high demands for energy and various biomaterials for biomass synthesis. As a result, enhanced catabolism (breakdown of macromolecules for energy production) and anabolism (macromolecule synthesis from bio-precursors) are induced in cancer. This phenomenon is called "metabolic reprogramming," a cancer hallmark contributing to cancer development, metastasis, and drug resistance. HCC and cholangiocarcinoma (CCA) are 2 different liver cancers with high intertumoral heterogeneity in terms of etiologies, mutational landscapes, transcriptomes, and histological representations. In agreement, metabolism in HCC or CCA is remarkably heterogeneous, although changes in the glycolytic pathways and an increase in the generation of lactate (the Warburg effect) have been frequently detected in those tumors. For example, HCC tumors with activated β-catenin are addicted to fatty acid catabolism, whereas HCC tumors derived from fatty liver avoid using fatty acids. In this review, we describe common metabolic alterations in HCC and CCA as well as metabolic features unique for their subsets. We discuss metabolism of NAFLD as well, because NAFLD will likely become a leading etiology of liver cancer in the coming years due to the obesity epidemic in the Western world. Furthermore, we outline the clinical implication of liver cancer metabolism and highlight the computation and systems biology approaches, such as genome-wide metabolic models, as a valuable tool allowing us to identify therapeutic targets and develop personalized treatments for liver cancer patients.

Inhibition of the SREBP pathway prevents SARS-CoV-2 replication and inflammasome activation

SARS-CoV-2 induces major cellular lipid rearrangements, exploiting the host's metabolic pathways to replicate. Sterol regulatory element binding proteins (SREBPs) are a family of transcription factors that control lipid metabolism. SREBP1 is associated with the regulation of fatty acids, whereas SREBP2 controls cholesterol metabolism, and both isoforms are associated with lipid droplet (LD) biogenesis. Here, we evaluated the effect of SREBP in a SARS-CoV-2-infected lung epithelial cell line (Calu-3). We showed that SARS-CoV-2 infection induced the activation of SREBP1 and SREBP2 and LD accumulation. Genetic knockdown of both SREBPs and pharmacological inhibition with the dual SREBP activation inhibitor fatostatin promote the inhibition of SARS-CoV-2 replication, cell death, and LD formation in Calu-3 cells. In addition, we demonstrated that SARS-CoV-2 induced inflammasome-dependent cell death by pyroptosis and release of IL-1β and IL-18, with activation of caspase-1, cleavage of gasdermin D1, was also reduced by SREBP inhibition. Collectively, our findings help to elucidate that SREBPs are crucial host factors required for viral replication and pathogenesis. These results indicate that SREBP is a host target for the development of antiviral strategies.

Carbon dioxide regulates cholesterol levels through SREBP2

In mammals, O2 and CO2 levels are tightly regulated and are altered under various pathological conditions. While the molecular mechanisms that participate in O2 sensing are well characterized, little is known regarding the signaling pathways that participate in CO2 signaling and adaptation. Here, we show that CO2 levels control a distinct cellular transcriptional response that differs from mere pH changes. Unexpectedly, we discovered that CO2 regulates the expression of cholesterogenic genes in a SREBP2-dependent manner and modulates cellular cholesterol accumulation. Molecular dissection of the underlying mechanism suggests that CO2 triggers SREBP2 activation through changes in endoplasmic reticulum (ER) membrane cholesterol levels. Collectively, we propose that SREBP2 participates in CO2 signaling and that cellular cholesterol levels can be modulated by CO2 through SREBP2.

Identification of the novel role of sterol regulatory element binding proteins (SREBPs) in mechanotransduction and intraocular pressure regulation

Trabecular meshwork (TM) cells are contractile and mechanosensitive, and they aid in maintaining intraocular pressure (IOP) homeostasis. Lipids are attributed to modulating TM contractility, with poor mechanistic understanding. In this study using human TM cells, we identify the mechanosensing role of the transcription factors sterol regulatory element binding proteins (SREBPs) involved in lipogenesis. By constitutively activating SREBPs and pharmacologically inactivating SREBPs, we have mechanistically deciphered the attributes of SREBPs in regulating the contractile properties of TM. The pharmacological inhibition of SREBPs by fatostatin and molecular inactivation of SREBPs ex vivo and in vivo, respectively, results in significant IOP lowering. As a proof of concept, fatostatin significantly decreased the SREBPs responsive genes and enzymes involved in lipogenic pathways as well as the levels of the phospholipid, cholesterol, and triglyceride. Further, we show that fatostatin mitigated actin polymerization machinery and stabilization, and decreased ECM synthesis and secretion. We thus postulate that lowering lipogenesis in the TM outflow pathway can hold the key to lowering IOP by modifying the TM biomechanics.

Structure-activity relationship studies on vitamin D-based selective SREBP/SCAP inhibitor KK-052

Vitamin D3 metabolites block lipid biosynthesis by promoting degradation of the complex of sterol regulatory element-binding protein (SREBP) and SREBP cleavage-activating protein (SCAP) independent of their effects on the vitamin D receptor (VDR). We previously reported the development of KK-052, the first vitamin D-based SREBP inhibitor that mitigates hepatic lipid accumulation without VDR-mediated calcemic action in mice. Herein we extend our previous work to synthesize KK-052 analogues. Various substituents were introduced to the phenyl ring of KK-052, and two KK-052 analogues were found to exhibit more potent SREBP/SCAP inhibitory activity than KK-052, whereas they all lack VDR activity. These new KK-052 analogues may be suited for further development as VDR-silent SREBP/SCAP inhibitors.

SREBP inhibitors: an updated patent review for 2008-present

INTRODUCTION

Sterol regulatory element-binding proteins (SREBPs) are a family of membrane-binding transcription factors that activate genes encoding enzymes required for cholesterol and unsaturated fatty acid synthesis. Overactivation of SREBP is related to the occurrence and development of diabetes, nonalcoholic fatty liver, tumor, and other diseases. In the past period, many SREBP inhibitors have been found.

AREAS COVERED

This manuscript is a patent review of SREBP inhibitors. We searched 2008 to date for all data from the US patent database (https://www.uspto.gov/) and the European patent database (https://www.epo.org/) with 'SREBP' and 'inhibitor' as keywords and analyzed the search results.

EXPERT OPINION

Both synthetic and natural SREBP inhibitors have been reported. Despite the lack of cocrystal structure of SREBP inhibitor, the mechanisms of several compounds have been clarified. Importantly, some SREBP inhibitors have been proved to have good activity in preclinical studies. As the characteristics of lipid metabolism reprogramming in cardio-cerebrovascular diseases and tumors are gradually revealed, more and more attention will be focused on SREBP.

A novel signature incorporating lipid metabolism- and immune-related genes to predict the prognosis and immune landscape in hepatocellular carcinoma

Background

Liver hepatocellular carcinoma (LIHC) is a highly malignant tumor with high metastasis and recurrence rates. Due to the relation between lipid metabolism and the tumor immune microenvironment is constantly being elucidated, this work is carried out to produce a new prognostic gene signature that incorporates immune profiles and lipid metabolism of LIHC patients.

Methods

We used the "DEseq2" R package and the "Venn" R package to identify differentially expressed genes related to lipid metabolism (LRDGs) in LIHC. Additionally, we performed unsupervised clustering of LIHC patients based on LRDGs to identify their subgroups and immuno-infiltration and Gene Ontology (GO) enrichment analysis on the subgroups. Next, we employed multivariate, LASSO and univariate Cox regression analyses to determine variables and to create a prognostic profile on the basis of immune- and lipid metabolism-related differential genes (IRDGs and LRDGs). We separated patients into low- and high-risk groups in accordance with the best cut-off value of risk score. We conducted Decision Curve Analysis (DCA), Receiver Operating Characteristic curve analysis as a function of time as well as Survival Analysis to evaluate this signature's prognostic value. We incorporated the clinical characteristics of patients into the risk model to obtain a nomogram prognostic model. GEO14520 and ICGC-LIRI JP datasets were employed to externally confirm the accuracy and robustness of signature. The gene set variation analysis (GSVA) and gene set enrichment analysis (GSEA) were applied for investigating the underlying mechanisms. Immune infiltration analysis was implemented to examine the differences in immune between both risk groups. Single-cell RNA sequencing (scRNA-SEQ) was utilized to characterize the genes that were involved in the distribution of signature and expression characteristics of different LIHC cell types. The patients' sensitivity in both risk groups to commonly used chemotherapeutic agents and semi-inhibitory concentrations (IC50) of the drugs was assessed using the GDSC database. On the basis of the differentially expressed genes (DEGs) in the two groups, the CMAP database was adopted for the prediction of potential small-molecule compounds. Small-molecule compounds were molecularly docked with prognostic markers. Lastly, we investigated the prognostic gene expression levels in normal and LIHC tissues with immunohistochemistry (IHC) and quantitative reverse transcription polymerase chain reaction(qRT-PCR).

Results

We built and verified a prognostic signature with seven genes that incorporated immune profiles and lipid metabolism. Patients were classified as low- and high-risk groups depending on their prognostic profiles. The overall survival (OS) was markedly lower in the high-risk group as compared to low-risk group. Time-dependent ROC curves more precisely predicted patients' survival at 1, 3 and 5 years; the area under the ROC curve was 0.81 (1 year), 0.75 (3 years) and 0.77 (5 years). The DCA curves showed the value of the prognostic genes in this signature for clinical applications. We included the patients' clinical characteristics in the risk model for both multivariate and univariate Cox regression analyses, and the findings revealed that the risk model represents an independent factor that influences OS in LIHC patients. With immune analysis, GSVA and GSEA, we identified that there are remarkable differences between the two risk groups in immune pathways, lipid metabolism, tumor development, immune cell infiltration and immune microenvironment, response to immunotherapy, and sensitivity to chemotherapy. Moreover, those with higher risk scores presented greater sensitivity to the chemotherapeutic agents. Experiments in vitro further elucidated the roles of SPP1 and FLT3 in the LIHC immune microenvironment. Furthermore, four small-molecule drugs that could target LIHC were screened. In vitro qRT-PCR , IHC revealed that the SPP1,KIF18A expressions were raised in LIHC in tumor samples, whereas FLT3,SOCS2 showed the opposite trend.

Conclusions

We developed and verified a new signature comprising immune- and lipid metabolism-associated markers and to assess the prognosis and the immune status of LIHC patients. This signature can be applied to survival prediction, individualized chemotherapy, and immunotherapeutic guidance for patients with liver cancer. This study also provides potential targeted therapeutics and novel ideas for the immune evasion and progression of LIHC.

Identification of the novel role of sterol regulatory element binding proteins (SREBPs) in mechanotransduction and intraocular pressure regulation

Trabecular meshwork (TM) cells are highly contractile and mechanosensitive to aid in maintaining intraocular pressure (IOP) homeostasis. Lipids are attributed to modulating TM contractility with poor mechanistic understanding. In this study using human TM cells, we identify the mechanosensing role of the transcription factors sterol regulatory element binding proteins (SREBPs) involved in lipogenesis. By constitutively activating SREBPs and pharmacologically inactivating SREBPs, we have mechanistically deciphered the attributes of SREBPs in regulating the contractile properties of TM. The pharmacological inhibition of SREBPs by fatostatin and molecular inactivation of SREBPs ex vivo and in vivo respectively results in significant IOP lowering. As a proof of concept, fatostatin significantly decreased the SREBPs responsive genes and enzymes involved in lipogenic pathways as well as the levels of the phospholipid, cholesterol, and triglyceride. Further, we show that fatostatin mitigated actin polymerization machinery and stabilization, and decreased ECM synthesis and secretion. We thus postulate that lowering lipogenesis in the TM outflow pathway can hold the key to lowering IOP by modifying the TM biomechanics.

Synopsis

In this study, we show the role of lipogenic transcription factors sterol regulatory element binding proteins (SREBPs) in the regulation of intraocular pressure (IOP). ( Synopsis Figure - Created using Biorender.com ) SREBPs are involved in the sensing of changes in mechanical stress on the trabecular meshwork (TM). SREBPs aid in transducing the mechanical signals to induce actin polymerization and filopodia/lamellipodia formation.SREBPs inactivation lowered genes and enzymes involved in lipogenesis and modified lipid levels in TM.SREBPs activity is a critical regulator of ECM engagement to the matrix sites.Inactivation of SCAP-SREBP pathway lowered IOP via actin relaxation and decreasing ECM production and deposition in TM outflow pathway signifying a novel relationship between SREBP activation status and achieving IOP homeostasis.

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.

Key events in cancer: Dysregulation of SREBPs

Lipid metabolism reprogramming is an important hallmark of tumor progression. Cancer cells require high levels of lipid synthesis and uptake not only to support their continued replication, invasion, metastasis, and survival but also to participate in the formation of biological membranes and signaling molecules. Sterol regulatory element binding proteins (SREBPs) are core transcription factors that control lipid metabolism and the expression of important genes for lipid synthesis and uptake. A growing number of studies have shown that SREBPs are significantly upregulated in human cancers and serve as intermediaries providing a mechanistic link between lipid metabolism reprogramming and malignancy. Different subcellular localizations, including endoplasmic reticulum, Golgi, and nucleus, play an indispensable role in regulating the cleavage maturation and activity of SREBPs. In this review, we focus on the relationship between aberrant regulation of SREBPs activity in three organelles and tumor progression. Because blocking the regulation of lipid synthesis by SREBPs has gradually become an important part of tumor therapy, this review also summarizes and analyzes several current mainstream strategies.

Tim-4 reprograms cholesterol metabolism to suppress antiviral innate immunity by disturbing the Insig1-SCAP interaction in macrophages

Accumulating evidence indicates that macrophages reshape their cholesterol metabolism in response to pathogens to support host defense. Intervention of host cholesterol homeostasis has emerged as a promising strategy for antiviral therapy. T cell immunoglobulin and mucin domain-containing molecule 4 (Tim-4) is indispensable in maintaining the homeostasis of macrophages. However, its role in antiviral innate immunity and cholesterol metabolism remains unknown. Here, we report that Tim-4 deficiency results in boosted interferon (IFN) signaling and decreased viral load. Mechanistically, Tim-4 disturbs the Insig1-SCAP interaction and promotes SCAP-SREBP2 complex translocation to the Golgi apparatus, eventually leading to the upregulation of cholesterol biosynthesis in macrophages, which limits the type I IFN response. Our findings demonstrate that Tim-4 suppresses type I IFN signaling by enhancing SREBP2 activation, delineating the role of Tim-4 in antiviral innate immunity and cholesterol metabolism, which sheds light on the mechanism by which Tim-4 orchestrates macrophage homeostasis.

Druggable Metabolic Vulnerabilities Are Exposed and Masked during Progression to Castration Resistant Prostate Cancer

There is an urgent need for exploring new actionable targets other than androgen receptor to improve outcome from lethal castration-resistant prostate cancer. Tumor metabolism has reemerged as a hallmark of cancer that drives and supports oncogenesis. In this regard, it is important to understand the relationship between distinctive metabolic features, androgen receptor signaling, genetic drivers in prostate cancer, and the tumor microenvironment (symbiotic and competitive metabolic interactions) to identify metabolic vulnerabilities. We explore the links between metabolism and gene regulation, and thus the unique metabolic signatures that define the malignant phenotypes at given stages of prostate tumor progression. We also provide an overview of current metabolism-based pharmacological strategies to be developed or repurposed for metabolism-based therapeutics for castration-resistant prostate cancer.

PIDDosome-SCAP crosstalk controls high-fructose-diet-dependent transition from simple steatosis to steatohepatitis

Sterol deficiency triggers SCAP-mediated SREBP activation, whereas hypernutrition together with ER stress activates SREBP1/2 via caspase-2. Whether these pathways interact and how they are selectively activated by different dietary cues are unknown. Here, we reveal regulatory crosstalk between the two pathways that controls the transition from hepatosteatosis to steatohepatitis. Hepatic ER stress elicited by NASH-inducing diets activates IRE1 and induces expression of the PIDDosome subunits caspase-2, RAIDD, and PIDD1, along with INSIG2, an inhibitor of SCAP-dependent SREBP activation. PIDDosome assembly activates caspase-2 and sustains IRE1 activation. PIDDosome ablation or IRE1 inhibition blunt steatohepatitis and diminish INSIG2 expression. Conversely, while inhibiting simple steatosis, SCAP ablation amplifies IRE1 and PIDDosome activation and liver damage in NASH-diet-fed animals, effects linked to ER disruption and preventable by IRE1 inhibition. Thus, the PIDDosome and SCAP pathways antagonistically modulate nutrient-induced hepatic ER stress to control non-linear transition from simple steatosis to hepatitis, a key step in NASH pathogenesis.

Concomitant Inhibition of FASN and SREBP Provides a Promising Therapy for CTCL

Simple Summary

The biosynthesis of fatty acids catalysed by FASN plays an important oncogenic role in various malignancies but has not been reported in CTCL yet. Here, we show that FASN is highly expressed in both cell lines and primary cells from CTCL patients. The inhibition of FASN impairs cell viability, survival, and proliferation. FASN expression is partly controlled by SREBP, and dual inhibition of FASN and SREBP enhances the impairment of cell proliferation. Overall, our data suggest that the combination of FASN and SREBP inhibitors could be a promising novel strategy in CTCL therapy.

Abstract

Cutaneous T cell lymphoma (CTCL) is a group of non-Hodgkin’s primary cutaneous T cell lymphomas, with Mycosis Fungoides and Sézary syndrome (SS) being the two most common subtypes. Fatty acid synthase (FASN) is a crucial enzyme that catalyses the biosynthesis of fatty acids, which has been reported to play an oncogenic role in various malignancies but not in CTCL so far. Herein, we show that FASN is highly expressed in CTCL cell lines and in peripheral blood mononuclear cells (PBMCs) from CTCL patients, while it is not in PBMCs from healthy individuals. The inhibition of FASN in CTCL cell lines impairs cell viability, survival, and proliferation, but, interestingly, it also increases FASN expression. However, inhibiting sterol regulatory element binding protein (SREBP), a transcription factor that promotes the expression of FASN, partially reversed the upregulation of FASN induced by FASN inhibitors. Thus, the combination of FASN and SREBP inhibitors enhanced the effects on both CTCL cell lines and PBMCs from SS patients, where a valid inhibition on cell proliferation could be verified. Importantly, compared to non-malignant cells, primary malignant cells are more sensitive to the inhibition of FASN and SREBP, making the combination of FASN and SREBP inhibitors a promising novel therapeutic strategy in CTCL.

GDNF regulates lipid metabolism and glioma growth through RET/ERK/HIF‑1/SREBP‑1

Cancer cells rewire their metabolism to meet the demands of growth and survival and this metabolic reprogramming has been recognized as an emerging hallmark of cancer. However, the respective mechanisms remain elusive and the contribution of aberrant lipid metabolism to the malignant phenotypes of glioma are unclear. The present study demonstrated that glial-derived neurotrophic factor (GDNF) is highly expressed in glioma and associated with poor clinical outcomes. In addition, there was a significant correlation between GDNF/rearranged during transfection (RET)/ERK signaling and sterol regulatory element-binding protein-1 (SREBP-1) expression in glioma cells. Pharmacological or genetic inhibition of GDNF-induced RET/ERK activity downregulated SREBP-1 expression and SREBP-1-mediated transcription of lipogenic genes. Additionally, GDNF regulated SREBP-1 activity by promoting hypoxia-inducible factor-1α (HIF-1α) mediated glucose absorption and hexosamine biosynthetic pathway mediated SREBP cleavage-activating protein N-glycosylation. In addition, the inhibition of SREBP-1 reduced the in vitro GDNF-induced glioma cell proliferation. The results elucidated the complex relationship between GDNF/RET/ERK signaling and dysregulated glycolipid-metabolism, which shows great potential to uncover novel metabolic vulnerabilities and improve the efficacy of targeted therapies.

Insulin can up-regulate LC-PUFA biosynthesis with the involvement of Srebp-1c and stimulatory protein 1 (Sp1) in marine teleost Siganus canaliculatus

The rabbitfish Siganus canaliculatus is the first marine teleost found to have the biosynthetic ability of long-chain polyunsaturated fatty acids (LC-PUFA) from C₁₈ precursors catalyzed by fatty acyl desaturases (Δ6/Δ5 Fads, Δ4 Fads) and elongases of very long chain fatty acids (Elovls). Previously, we predicted the existence of insulin (INS) response elements (IREs) including nuclear factor Y (NF-Y) and sterol regulatory element (SRE) in the core promoter region of rabbitfish Δ6/Δ5 fads and Δ4 fads. To clarify the potential regulatory effect and mechanism of INS in LC-PUFA biosynthesis, INS responding region was identified at -456 bp to + 51 bp of Δ6/Δ5 fads core promoter, but not in Δ4 fads promoter. Moreover, a unique stimulatory protein 1 (Sp1) element was predicted in the INS responding region of Δ6/Δ5 fads. Subsequently, SRE, NF-Y and Sp1 elements were proved as IREs in Δ6/Δ5 fads promoter. The up-regulation of INS on gene expression of Srebp-1c, Sp1, Δ6/Δ5 fads and elovl5 as well as the LC-PUFA biosynthesis was further demonstrated in S. canaliculatus hepatocyte line (SCHL) cells, but no influence was detected on Δ4 fads. Besides, inhibitors of transcription factors Srebp-1c (Fatostatin, PF-429242) and Sp1 (Mithramycin) could inhibit the gene expression of Srebp-1c, Δ6/Δ5 fads and elovl5, and abolish the up-regulation of INS on these genes' expression and LC-PUFA biosynthesis. These results indicated that INS could up-regulate LC-PUFA biosynthesis with the involvement of Srebp-1c and Sp1 in rabbitfish S. canaliculatus, which is the first report in teleost.

Pectolinarigenin reduces the expression of sterol regulatory element-binding proteins and cellular lipid levels

Sterol regulatory element-binding proteins (SREBPs) are transcription factors that act important roles in the genes involved in lipid biosynthesis. In this study, it was found that the flavonoid pectolinarigenin, reduced the activity of SRE-containing fatty acid synthase (FAS) promoter and the mRNA expressions of SREBP target genes in human hepatoma (Huh-7) cells. Moreover, compared to other flavonoids, pectolinarigenin reduced the mature forms of SREBPs in a dose-dependent manner. The insulin-induced gene (INSIG) and proteasome were not involved in the pectolinarigenin-mediated reduction of mature forms of SREBPs. Pectolinarigenin also reduced the lipid contents in vitro. These results suggest that pectolinarigenin may inhibit lipogenesis through suppressing SREBP activity, at least partially, via the formation of SREBPs mature forms, thereby reducing the expression of their downstream genes related to lipogenesis. To the best of our knowledge, this is the first work that shows how pectolinarigenin affects cellular lipid levels by affecting SREBPs.

Counteracting Health Risks by Modulating Homeostatic Signaling

Homeostasis was initially conceptualized by Bernard and Cannon around a century ago as a steady state of physiological parameters that vary within a certain range, such as blood pH, body temperature, and heart rate^1,2. The underlying mechanisms that maintain homeostasis are explained by negative feedbacks that are executed by the neuronal, endocrine, and immune systems. At the cellular level, homeostasis, such as that of redox and energy steady state, also exists and is regulated by various cell signaling pathways. The induction of homeostatic mechanism is critical for human to adapt to various disruptive insults (stressors); while on the other hand, adaptation occurs at the expense of other physiological processes and thus runs the risk of collateral damages, particularly under conditions of chronic stress. Conceivably, anti-stress protection can be achieved by stressor-mimicking medicinals that elicit adaptive responses prior to an insult and thereby serve as health risk countermeasures; and in situations where maladaptation may occur, downregulating medicinals could be used to suppress the responses and prevent subsequent pathogenesis. Both strategies are preemptive interventions particularly suited for individuals who carry certain lifestyle, environmental, or genetic risk factors. In this article, we will define and characterize a new modality of prophylactic intervention that forestalls diseases via modulating homeostatic signaling. Moreover, we will provide evidence from the literature that support this concept and distinguish it from other homeostasis-related interventions such as adaptogen, hormesis, and xenohormesis.