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.

SPRING licenses S1P-mediated cleavage of SREBP2 by displacing an inhibitory pro-domain.

Site-one protease (S1P) conducts the first of two cleavage events in the Golgi to activate Sterol regulatory element binding proteins (SREBPs) and upregulate lipogenic transcription. S1P is also required for a wide array of additional signaling pathways. A zymogen serine protease, S1P matures through autoproteolysis of two pro-domains, with one cleavage event in the endoplasmic reticulum (ER) and the other in the Golgi. We recently identified the SREBP regulating gene, (SPRING), which enhances S1P maturation and is necessary for SREBP signaling. Here, we report the cryo-EM structures of S1P and S1P-SPRING at sub-2.5 Å resolution. SPRING activates S1P by dislodging its inhibitory pro-domain and stabilizing intra-domain contacts. Functionally, SPRING licenses S1P to cleave its cognate substrate, SREBP2. Our findings reveal an activation mechanism for S1P and provide insights into how spatial control of S1P activity underpins cholesterol homeostasis.

PKMYT1 knockdown inhibits cholesterol biosynthesis and promotes the drug sensitivity of triple-negative breast cancer cells to atorvastatin.

Triple negative breast cancer (TNBC) as the most aggressive molecular subtype of breast cancer is characterized by high cancer cell proliferation and poor patient prognosis. Abnormal lipid metabolism contributes to the malignant process of cancers. Study observed significantly enhanced cholesterol biosynthesis in TNBC. However, the mechanisms underlying the abnormal increase of cholesterol biosynthesis in TNBC are still unclear. Hence, we identified a member of the serine/threonine protein kinase family PKMYT1 as a key driver of cholesterol synthesis in TNBC cells. Aberrantly high-expressed PKMYT1 in TNBC was indicative of unfavorable prognostic outcomes. In addition, PKMYT1 promoted sterol regulatory element-binding protein 2 (SREBP2)-mediated expression of enzymes related to cholesterol biosynthesis through activating the TNF/ TNF receptor-associated factor 1 (TRAF1)/AKT pathway. Notably, downregulation of PKMYT1 significantly inhibited the feedback upregulation of statin-mediated cholesterol biosynthesis, whereas knockdown of PKMYT1 promoted the drug sensitivity of atorvastatin in TNBC cells. Overall, our study revealed a novel function of PKMYT1 in TNBC cholesterol biosynthesis, providing a new target for targeting tumor metabolic reprogramming in the cancer.

20( S )-Protopanaxatriol Improves Atherosclerosis by Inhibiting Low-Density Lipoprotein Receptor Degradation in ApoE KO Mice.

ABSTRACT: Atherosclerosis (AS) is a chronic progressive disease caused by various factors and causes various cerebrovascular and cardiovascular diseases (CVDs). Reducing the plasma levels of low-density lipoprotein cholesterol is the primary goal in preventing and treating AS. Proprotein convertase subtilisin/kexin type 9 (PCSK9) plays a crucial role in regulating low-density lipoprotein cholesterol metabolism. Panax notoginseng has potent lipid-reducing effects and protects against CVDs, and its saponins induce vascular dilatation, inhibit thrombus formation, and are used in treating CVDs. However, the anti-AS effect of the secondary metabolite, 20( S )-protopanaxatriol (20( S )-PPT), remains unclear. In this study, the anti-AS effect and molecular mechanism of 20( S )-PPT were investigated in vivo and in vitro by Western blotting, real-time polymerase chain reaction, enzyme-linked immunosorbent assay, immunofluorescence staining, and other assays. The in vitro experiments revealed that 20( S )-PPT reduced the levels of PCSK9 in the supernatant of HepG2 cells, upregulated low-density lipoprotein receptor protein levels, promoted low-density lipoprotein uptake by HepG2 cells, and reduced PCSK9 mRNA transcription by upregulating the levels of forkhead box O3 protein and mRNA and decreasing the levels of HNF1α and SREBP2 protein and mRNA. The in vivo experiments revealed that 20( S )-PPT upregulated aortic α-smooth muscle actin expression, increased the stability of atherosclerotic plaques, and reduced aortic plaque formation induced by a high-cholesterol diet in ApoE -/- mice (high-cholesterol diet-fed group). Additionally, 20( S )-PPT reduced the aortic expression of CD68, reduced inflammation in the aortic root, and alleviated the hepatic lesions in the high-cholesterol diet-fed group. The study revealed that 20( S )-PPT inhibited low-density lipoprotein receptor degradation via PCSK9 to alleviate AS.

Mitochondrial translation failure represses cholesterol gene expression via Pyk2-Gsk3ß-Srebp2 axis.

Neurodegenerative diseases and other age-related disorders are closely associated with mitochondrial dysfunction. We previously showed that mice with neuron-specific deficiency of mitochondrial translation exhibit leukoencephalopathy because of demyelination. Reduced cholesterol metabolism has been associated with demyelinating diseases of the brain such as Alzheimer's disease. However, the molecular mechanisms involved and relevance to the pathogenesis remained unknown. In this study, we show that inhibition of mitochondrial translation significantly reduced expression of the cholesterol synthase genes and degraded their sterol-regulated transcription factor, sterol regulatory element-binding protein 2 (Srebp2). Furthermore, the phosphorylation of Pyk2 and Gsk3ß was increased in the white matter of p32cKO mice. We observed that Pyk2 inhibitors reduced the phosphorylation of Gsk3ß and that GSK3ß inhibitors suppressed degradation of the transcription factor Srebp2. The Pyk2-Gsk3ß axis is involved in the ubiquitination of Srebp2 and reduced expression of cholesterol gene. These results suggest that inhibition of mitochondrial translation may be a causative mechanism of neurodegenerative diseases of aging. Improving the mitochondrial translation or effectiveness of Gsk3ß inhibitors is a potential therapeutic strategy for leukoencephalopathy.

A lactate-SREBP2 signaling axis drives tolerogenic dendritic cell maturation and promotes cancer progression.

Conventional dendritic cells (DCs) are essential mediators of antitumor immunity. As a result, cancers have developed poorly understood mechanisms to render DCs dysfunctional within the tumor microenvironment (TME). After identification of CD63 as a specific surface marker, we demonstrate that mature regulatory DCs (mregDCs) migrate to tumor-draining lymph node tissues and suppress DC antigen cross-presentation in trans while promoting T helper 2 and regulatory T cell differentiation. Transcriptional and metabolic studies showed that mregDC functionality is dependent on the mevalonate biosynthetic pathway and its master transcription factor, SREBP2. We found that melanoma-derived lactate activates SREBP2 in tumor DCs and drives conventional DC transformation into mregDCs via homeostatic or tolerogenic maturation. DC-specific genetic silencing and pharmacologic inhibition of SREBP2 promoted antitumor CD8+ T cell activation and suppressed melanoma progression. CD63+ mregDCs were found to reside within the lymph nodes of several preclinical tumor models and in the sentinel lymph nodes of patients with melanoma. Collectively, this work suggests that a tumor lactate-stimulated SREBP2-dependent program promotes CD63+ mregDC development and function while serving as a promising therapeutic target for overcoming immune tolerance in the TME.

LY86 facilitates ox-LDL-induced lipid accumulation in macrophages by upregulating SREBP2/HMGCR expression.

LY86, also known as MD1, has been implicated in various pathophysiological processes including inflammation, obesity, insulin resistance, and immunoregulation. However, the role of LY86 in cholesterol metabolism remains incompletely understood. Several studies have reported significant up-regulation of LY86 mRNA in atherosclerosis; nevertheless, the regulatory mechanism by which LY86 is involved in this disease remains unclear. In this study, we aimed to investigate whether LY86 affects ox-LDL-induced lipid accumulation in macrophages. Firstly, we confirmed that LY86 is indeed involved in the process of atherosclerosis and found high expression levels of LY86 in human atherosclerotic plaque tissue. Furthermore, our findings suggest that LY86 may mediate intracellular lipid accumulation induced by ox-LDL through the SREBP2/HMGCR pathway. This mechanism could be associated with increased cholesterol synthesis resulting from enhanced endoplasmic reticulum stress response.

ALOX15B controls macrophage cholesterol homeostasis via lipid peroxidation, ERK1/2 and SREBP2.

Macrophage cholesterol homeostasis is crucial for health and disease and has been linked to the lipid-peroxidizing enzyme arachidonate 15-lipoxygenase type B (ALOX15B), albeit molecular mechanisms remain obscure. We performed global transcriptome and immunofluorescence analysis in ALOX15B-silenced primary human macrophages and observed a reduction of nuclear sterol regulatory element-binding protein (SREBP) 2, the master transcription factor of cellular cholesterol biosynthesis. Consequently, SREBP2-target gene expression was reduced as were the sterol biosynthetic intermediates desmosterol and lathosterol as well as 25- and 27-hydroxycholesterol. Mechanistically, suppression of ALOX15B reduced lipid peroxidation in primary human macrophages and thereby attenuated activation of mitogen-activated protein kinase ERK1/2, which lowered SREBP2 abundance and activity. Low nuclear SREBP2 rendered both, ALOX15B-silenced and ERK1/2-inhibited macrophages refractory to SREBP2 activation upon blocking the NPC intracellular cholesterol transporter 1. These studies suggest a regulatory mechanism controlling macrophage cholesterol homeostasis based on ALOX15B-mediated lipid peroxidation and concomitant ERK1/2 activation.

Tanshinone IIA acts as a regulator of lipogenesis to overcome osimertinib acquired resistance in lung cancer.

Osimertinib is a novel epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI), acting as the first-line medicine for advanced EGFR-mutated NSCLC. Recently, the acquired resistance to osimertinib brings great challenges to the advanced treatment. Therefore, it is in urgent need to find effective strategy to overcome osimertinib acquired resistance. Here, we demonstrated that SREBP pathway-driven lipogenesis was a key mediator to promote osimertinib acquired resistance, and firstly found Tanshinone IIA (Tan IIA), a natural pharmacologically active constituent isolated from Salvia miltiorrhiza, could overcome osimertinib-acquired resistance in vitro and in vivo via inhibiting SREBP pathway-mediated lipid lipogenesis by using LC-MS based cellular lipidomics analysis, quantitative real-time PCR (qRT-PCR) analysis, western blotting analysis, flow cytometry, small interfering RNAs transfection, and membrane fluidity assay et al. The results showed that SREBP1/2-driven lipogenesis was highly activated in osimertinib acquired resistant NSCLC cells, while knockdown or inhibition of SREBP1/2 could restore the sensitivity of NSCLC to osimertinib via altered the proportion of saturated phospholipids and unsaturated phospholipids in osimertinib acquired-resistant cells. Furthermore, Tanshinone IIA (Tan IIA) could reverse the acquired resistance to osimertinib in lung cancer. Mechanically, Tan IIA inhibited SREBP signaling mediated lipogenesis, changed the profiles of saturated phospholipids and unsaturated phospholipids, and thus promoted osimertinib acquired resistant cancer cells to be attacked by oxidative stress-induced damage and reduce the cell membrane fluidity. The reversal effect of Tan IIA on osimertinib acquired resistant NSCLC cells was also confirmed in vivo, which is helpful for the development of strategies to reverse osimertinib acquired resistance.

PRMT5 activates lipid metabolic reprogramming via MYC contributing to the growth and survival of mantle cell lymphoma.

Mantle cell lymphoma (MCL) is an incurable and aggressive subtype of non-Hodgkin B-cell lymphoma. Increased lipid uptake, storage, and lipogenesis occur in a variety of cancers and contribute to rapid tumor growth. However, no data has been explored for the roles of lipid metabolism reprogramming in MCL. Here, we identified aberrant lipid metabolism reprogramming and PRMT5 as a key regulator of cholesterol and fatty acid metabolism reprogramming in MCL patients. High PRMT5 expression predicts adverse outcome prognosis in 105 patients with MCL and GEO database (GSE93291). PRMT5 deficiency resulted in proliferation defects and cell death by CRISPR/Cas9 editing. Moreover, PRMT5 inhibitors including SH3765 and EPZ015666 worked through blocking SREBP1/2 and FASN expression in MCL. Furthermore, PRMT5 was significantly associated with MYC expression in 105 MCL samples and the GEO database (GSE93291). CRISPR MYC knockout indicated PRMT5 can promote MCL outgrowth by inducing SREBP1/2 and FASN expression through the MYC pathway.

Endothelial nucleotide-binding oligomerization domain-like receptor protein 3 inflammasome regulation in atherosclerosis.

AIMS: The activation of nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) inflammasome in endothelial cells (ECs) contributes to vascular inflammation in atherosclerosis. Considering the high glycolytic rate of ECs, we delineated whether and how glycolysis determines endothelial NLRP3 inflammasome activation in atherosclerosis. METHODS AND RESULTS: Our results demonstrated a significant up-regulation of 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3), a key regulator of glycolysis, in human and mouse atherosclerotic endothelium, which positively correlated with NLRP3 levels. Atherosclerotic stimuli up-regulated endothelial PFKFB3 expression via sterol regulatory element-binding protein 2 (SREBP2) transactivation. EC-selective haplodeficiency of Pfkfb3 in Apoe-/- mice resulted in reduced endothelial NLRP3 inflammasome activation and attenuation of atherogenesis. Mechanistic investigations revealed that PFKFB3-driven glycolysis increased the NADH content and induced oligomerization of C-terminal binding protein 1 (CtBP1), an NADH-sensitive transcriptional co-repressor. The monomer form, but not the oligomer form, of CtBP1 was found to associate with the transcriptional repressor Forkhead box P1 (FOXP1) and acted as a transrepressor of inflammasome components, including NLRP3, caspase-1, and interleukin-1ß (IL-1ß). Interfering with NADH-induced CtBP1 oligomerization restored its binding to FOXP1 and inhibited the glycolysis-dependent up-regulation of NLRP3, Caspase-1, and IL-1ß. Additionally, EC-specific overexpression of NADH-insensitive CtBP1 alleviates atherosclerosis. CONCLUSION: Our findings highlight the existence of a glycolysis-dependent NADH/CtBP/FOXP1-transrepression pathway that regulates endothelial NLRP3 inflammasome activation in atherogenesis. This pathway represents a potential target for selective PFKFB3 inhibitors or strategies aimed at disrupting CtBP1 oligomerization to modulate atherosclerosis.

METTL3 and METTL14-mediated N6-methyladenosine modification of SREBF2-AS1 facilitates hepatocellular carcinoma progression and sorafenib resistance through DNA demethylation of SREBF2.

As the most prevalent epitranscriptomic modification, N6-methyladenosine (m6A) shows important roles in a variety of diseases through regulating the processing, stability and translation of target RNAs. However, the potential contributions of m6A to RNA functions are unclear. Here, we identified a functional and prognosis-related m6A-modified RNA SREBF2-AS1 in hepatocellular carcinoma (HCC). The expression of SREBF2-AS1 and SREBF2 in HCC tissues and cells was measured by RT-qPCR. m6A modification level of SREBF2-AS1 was measured by methylated RNA immunoprecipitation assay. The roles of SREBF2-AS1 in HCC progression and sorafenib resistance were investigated by proliferation, apoptosis, migration, and cell viability assays. The regulatory mechanisms of SREBF2-AS1 on SREBF2 were investigated by Chromatin isolation by RNA purification, RNA immunoprecipitation, CUT&RUN, and bisulfite DNA sequencing assays. Our findings showed that the expression of SREBF2-AS1 was increased in HCC tissues and cells, and positively correlated with poor survival of HCC patients. m6A modification level of SREBF2-AS1 was also increased in HCC and positively correlated with poor prognosis of HCC patients. METTL3 and METTL14-induced m6A modification upregulated SREBF2-AS1 expression through increasing SREBF2-AS1 transcript stability. Functional assays showed that only m6A-modified, but not non-modified SREBF2-AS1 promoted HCC progression and sorafenib resistance. Mechanistic investigations revealed that m6A-modified SREBF2-AS1 bound and recruited m6A reader FXR1 and DNA 5-methylcytosine dioxygenase TET1 to SREBF2 promoter, leading to DNA demethylation at SREBF2 promoter and the upregulation of SREBF2 transcription. Functional rescue assays showed that SREBF2 was the critical mediator of the oncogenic roles of SREBF2-AS1 in HCC. Together, this study showed that m6A-modified SREBF2-AS1 exerted oncogenic roles in HCC through inducing DNA demethylation and transcriptional activation of SREBF2, and suggested m6A-modified SREBF2-AS1 as a prognostic biomarker and therapeutic target for HCC.

Relationships of brain cholesterol and cholesterol biosynthetic enzymes to Alzheimer's pathology and dementia in the CFAS population-derived neuropathology cohort.

Altered cholesterol metabolism is implicated in brain ageing and Alzheimer's disease. We examined whether key genes regulating cholesterol metabolism and levels of brain cholesterol are altered in dementia and Alzheimer's disease neuropathological change (ADNC). Temporal cortex (n = 99) was obtained from the Cognitive Function and Ageing Study. Expression of the cholesterol biosynthesis rate-limiting enzyme HMG-CoA reductase (HMGCR) and its regulator, SREBP2, were detected using immunohistochemistry. Expression of HMGCR, SREBP2, CYP46A1 and ABCA1 were quantified by qPCR in samples enriched for astrocyte and neuronal RNA following laser-capture microdissection. Total cortical cholesterol was measured using the Amplex Red assay. HMGCR and SREBP2 proteins were predominantly expressed in pyramidal neurones, and in glia. Neuronal HMGCR did not vary with ADNC, oxidative stress, neuroinflammation or dementia status. Expression of HMGCR neuronal mRNA decreased with ADNC (p = 0.022) and increased with neuronal DNA damage (p = 0.049), whilst SREBP2 increased with ADNC (p = 0.005). High or moderate tertiles for cholesterol levels were associated with increased dementia risk (OR 1.44, 1.58). APOE ε4 allele was not associated with cortical cholesterol levels. ADNC is associated with gene expression changes that may impair cholesterol biosynthesis in neurones but not astrocytes, whilst levels of cortical cholesterol show a weak relationship to dementia status.

Excess phosphate promotes SARS­CoV­2 N protein­induced NLRP3 inflammasome activation via the SCAP­SREBP2 signaling pathway.

Hyperphosphatemia or severe acute respiratory syndrome coronavirus 2 (SARS­CoV­2) infection can promote cardiovascular adverse events in patients with chronic kidney disease. Hyperphosphatemia is associated with elevated inflammation and sterol regulatory element binding protein 2 (SREBP2) activation, but the underlying mechanisms in SARS­CoV­2 that are related to cardiovascular disease remain unclear. The present study aimed to elucidate the role of excess inorganic phosphate (PI) in SARS­CoV­2 N protein­induced NLRP3 inflammasome activation and the underlying mechanisms in vascular smooth muscle cells (VSMCs). The expression levels of SARS­CoV­2 N protein, SREBP cleavage­activating protein (SCAP), mature N­terminal SREBP2, NLRP3, procaspase­1, cleaved caspase­1, IL­1ß and IL­18 were examined by western blotting. The expression levels of SREBP2, HMG­CoA reductase, HMGCS1, low density lipoprotein receptor, proprotein convertase subtilisin/kexin type 9 (PCSK9), SREBP1c, fatty acid synthase, stearyl coenzyme A desaturase 1, acetyl­CoA carboxylase α and ATP­citrate lyase were determined by reverse transcription­quantitative PCR. The translocation of SCAP or NLRP3 from the endoplasmic reticulum to the Golgi was detected by confocal microscopy. The results showed that excess PI promoted SCAP­SREBP and NLRP3 complex translocation to the Golgi, potentially leading to NLRP3 inflammasome activation and lipogenic gene expression. Furthermore, PI amplified SARS­CoV­2 N protein­induced inflammation via the SCAP­SREBP pathway, which facilitates NLRP3 inflammasome assembly and activation. Inhibition of phosphate uptake with phosphonoformate sodium alleviated NLRP3 inflammasome activation and reduced SREBP­mediated lipogenic gene expression in VSMCs stimulated with PI and with SARS­CoV­2 N protein overexpression. Inhibition of SREBP2 or small interfering RNA­induced silencing of SREBP2 effectively suppressed the effect of PI and SARS­CoV­2 N protein on NLRP3 inflammasome activation and lipogenic gene expression. In conclusion, the present study identified that PI amplified SARS­CoV­2 N protein­induced NLRP3 inflammasome activation and lipogenic gene expression via the SCAP­SREBP signaling pathway.

Dietary palm oil enhances Sterol regulatory element-binding protein 2-mediated cholesterol biosynthesis through inducing endoplasmic reticulum stress in muscle of large yellow croaker (Larimichthys crocea).

Sterol regulatory element-binding protein 2 (SREBP2) is considered to be a major regulator to control cholesterol homoeostasis in mammals. However, the role of SREBP2 in teleost remains poorly understand. Here, we explored the molecular characterisation of SREBP2 and identified SREBP2 as a key modulator for 3-hydroxy-3-methylglutaryl-coenzyme A reductase and 7-dehydrocholesterol reductase, which were rate-limiting enzymes of cholesterol biosynthesis. Moreover, dietary palm oil in vivo or palmitic acid (PA) treatment in vitro elevated cholesterol content through triggering SREBP2-mediated cholesterol biosynthesis in large yellow croaker. Furthermore, our results also found that PA-induced activation of SREBP2 was dependent on the stimulating of endoplasmic reticulum stress (ERS) in croaker myocytes and inhibition of ERS by 4-Phenylbutyric acid alleviated PA-induced SREBP2 activation and cholesterol biosynthesis. In summary, our findings reveal a novel insight for understanding the role of SREBP2 in the regulation of cholesterol metabolism in fish and may deepen the link between dietary fatty acid and cholesterol biosynthesis.

Cholesterol homeostasis confers glioma malignancy triggered by hnRNPA2B1-dependent regulation of SREBP2 and LDLR.

BACKGROUND: Dysregulation of cholesterol metabolism is a significant characteristic of glioma, yet the underlying mechanisms are largely unknown. N6-methyladenosine (m6A) modification has been implicated in promoting tumor development and progression. The aim of this study was to determine the key m6A regulatory proteins involved in the progression of glioma, which is potentially associated with the reprogramming of cholesterol homeostasis. METHODS: Bioinformatics analysis was performed to determine the association of m6A modification with glioma malignancy from The Cancer Genome Atlas and Genotype-Tissue Expression datasets. Glioma stem cell (GSC) self-renewal was determined by tumor sphere formation and bioluminescence image assay. RNA sequencing and lipidomic analysis were performed for cholesterol homeostasis analysis. RNA immunoprecipitation and luciferase reporter assay were performed to determine hnRNPA2B1-dependent regulation of sterol regulatory element-binding protein 2 (SREBP2) and low-density lipoprotein receptor (LDLR) mRNA. The methylation status of hnRNPA2B1 promoter was determined by bioinformatic analysis and methylation-specific PCR assay. RESULTS: Among the m6A-regulatory proteins, hnRNPA2B1 was demonstrated the most important independent prognostic risk factor for glioma. hnRNPA2B1 ablation exhibited a significant tumor-suppressive effect on glioma cell proliferation, GSC self-renewal and tumorigenesis. hnRNPA2B1 triggers de novo cholesterol synthesis by inducing HMGCR through the stabilization of SREBP2 mRNA. m6A modification of SREBP2 or LDLR mRNA is required for hnRNPA2B1-mediated mRNA stability. The hypomethylation of cg21815882 site on hnRNPA2B1 promoter confers elevated expression of hnRNPA2B1 in glioma tissues. The combination of targeting hnRNPA2B1 and cholesterol metabolism exhibited remarkable antitumor effects, suggesting valuable clinical implications for glioma treatment. CONCLUSIONS: hnRNPA2B1 facilitates cholesterol uptake and de novo synthesis, thereby contributing to glioma stemness and malignancy.

The RORÉ£/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.

High-salt diet induces dyslipidemia through the SREBP2/PCSK9 pathway in dahl salt-sensitive rats.

A high-salt diet is known to increase serum cholesterol levels; however, the underlying mechanism of salt-induced dyslipidemia in patients with salt-sensitivity remains poorly understood. We aimed to investigate whether high-salt diet (HSD) can induce dyslipidemia and elucidate the underlying mechanism of salt-induced dyslipidemia in Dahl salt-sensitive (SS) rats. Metabolomic and biochemical analyses revealed that the consumption of an HSD (8 % NaCl) significantly increased the serum levels of total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) in SS rats. The enzyme-linked immunosorbent assay demonstrated an increase in circulating proprotein convertase subtilisin/kexin type 9 (PCSK9) levels, accompanied by a decrease in hepatic low-density lipoprotein receptor (LDLR) levels due to HSD consumption. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and Western blot analysis revealed that HSD consumption activated sterol regulatory element-binding protein-2 (SREBP2) expression in the liver and kidney, resulting in upregulation of PCSK9 at the transcriptional level in the liver and at the translational level in the kidney, ultimately increasing circulating PCSK9 levels. The combined effects of HSD on the liver and kidney contributed to the development of hypercholesterolemia. Furthermore, an in vitro assay confirmed that high-salt exposure led to an increase in the protein expression of SREBP2 and PCSK9 secretion, thereby reducing low-density lipoprotein (LDL) uptake. This study, for the first time, shows that an HSD induces dyslipidemia through activation of the SREBP2/PCSK9 pathway, providing new insights into the prevention and treatment of dyslipidemia in patients with salt sensitivity.

Chlorogenic acid regulates the expression of NPC1L1 and HMGCR through PXR and SREBP2 signaling pathways and their interactions with HSP90 to maintain cholesterol homeostasis.

BACKGROUND: Hypercholesterolemia is widely implicated in the etiology of coronary heart disease, stroke, and dementia. Evidence suggests that chlorogenic acid (CA) reduces the risk of cardiovascular disease. PURPOSE: The current study aims to explore the underlying molecular mechanism of CA in lowering cholesterol based on pregnane X receptor (PXR) and sterol regulatory element-binding protein 2 (SREBP2) regulatory pathways and their interactions with heat shock protein 90 (HSP90). METHODS: A hypercholesterolemic mouse model, HepG2 and Caco2 cell models, metabolomics analysis, and co-immunoprecipitation (COIP) were used to study the mechanism of CA lowering cholesterol. RESULTS: Treatment of the hypercholesterolemic mice with CA for 12 weeks significantly reduced body weight, blood lipid, hepatic lipid accumulation, and increased lipid excretion. The nuclear aggregation of PXR and SREBP2 was inhibited simultaneously. In addition, the expression of downstream target genes, including Niemann-pick C1-like 1 (NPC1L1) and 3­hydroxy-3-methylglutaryl-CoA reductase (HMGCR), was downregulated after CA administration. Furthermore, in HepG2 and Caco2 cell models, CA reduced intracellular cholesterol levels by inhibiting the nuclear translocation of PXR and SREBP2 and the expression of NPC1L1 and HMGCR. SREBP2 interacts with PXR through HSP90, and CA reduces the binding stability of SREBP2 and HSP90 and enhances the binding of PXR and HSP90, thus reducing the nuclear accumulation of SREBP2 and PXR simultaneously. Moreover, CA promoted the phosphorylation of AMP-activated protein kinase (AMPK) and its binding to SREBP2. This was not conducive to the binding of HSP90 and SREBP2 but enhanced the binding of HSP90 and PXR, thereby inhibiting the nuclear translocation of SREBP2 and PXR and reducing intracellular cholesterol levels. However, no noticeable direct binding between AMPK and PXR was observed. CONCLUSION: CA downregulates NPC1L1 and HMGCR expression by acting on the AMPK/SREBP2 direct pathway and the AMPK/SREBP2/HSP90/PXR indirect pathway, thus retaining cholesterol homeostasis.

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.