Regulation Of Cholesterol Homeostasis Research Articles

Tumor-derived miR-9-5p-loaded EVs regulate cholesterol homeostasis to promote breast cancer liver metastasis in mice

Cancer cells secrete extracellular vesicles (EV) encapsulating bioactive cargoes to facilitate inter-organ communication in vivo and are emerging as critical mediators of tumor progression and metastasis, a condition which is often accompanied by a dysregulated cholesterol metabolism. Whether EVs are involved in the control of cholesterol homeostasis during tumor metastasis is still undefined and warrant further investigation. Here, we find that breast cancer-derived exosomal miR-9-5p induces the expression of HMGCR and CH25H, two enzymes involved in cholesterol synthesis and the conversion of 25-hydroxycholesterol from cholesterol by targeting INSIG1, INSIG2 and ATF3 genes in the liver. Notably, in vivo miR-9-5p antagomir treatment and genetic CH25H ablation prevents tumor metastasis in a mouse model of breast cancer. Thus, our findings reveal the regulatory mechanism of tumor-derived miR-9-5p in liver metastasis by linking oxysterol metabolism and Kupffer cell polarization, shedding light on future applications for cancer diagnosis and treatment.

Abstract C027: The role of Liver Receptor Homolog 1 (LRH-1) in regulating cancer progression by modulating the immune response

Abstract Breast cancer is a significant global health concern, being the second most common type of cancer and the second leading cause of cancer-related deaths among women in the U.S. Metastatic breast cancer is responsible for most of these deaths, and current FDA-approved immunotherapies are effective only for a small subset of patients with PD-L1-positive tumors. Thus, there is a critical need for new therapeutic targets to enhance the immune response against breast cancer. Elevated plasma cholesterol concentrations are associated with poor breast cancer outcomes. Our previous studies indicated that myeloid immune cells are highly sensitive to changes in cholesterol levels and other proteins involved in regulating cholesterol homeostasis. However, the role of Liver Receptor Homolog 1 (LRH-1), a key regulator of cholesterol homeostasis, in myeloid cells is not well understood. Notably, higher expression of LRH-1 mRNA in breast tumors is associated with longer time to recurrence and improved overall survival. Therefore, we aimed to investigate the role of LRH-1 in myeloid immune cells and its impact on breast cancer progression. Initial analysis indicated that LRH-1 is expressed in myeloid cells, with particularly high levels observed in neutrophils. Therefore, we examined how LRH-1 regulates neutrophil functions important to cancer biology, including migration, NETosis, and phagocytosis, as well as its influence through neutrophils on T cells. We found that LRH-1 inhibited neutrophil migration toward cancer cells. Since tumor infiltrating neutrophils are generally associated with poor prognosis, LRH-1 reducing neutrophil migration could indicate a decreased ability of these immune-suppressive cells to infiltrate tumors. Importantly, neutrophils treated with an LRH-1 agonist showed reduced NETosis, while antagonist led to increased NETosis. LRH-1 agonist treatment also significantly reduced neutrophil phagocytosis, whereas an antagonist had no notable effect. Furthermore, T cells exhibited increased expansion when co-cultured with neutrophils treated with an LRH-1 agonist, and reduced proliferation with neutrophils pretreated with an LRH-1 antagonist or inverse agonist, particularly in CD4+ helper T cells and later divisions. Since neutrophils were previously implicated in invoking recurrence from dormant lesions, we evaluated LRH-1 in this context. The treatment of mice harboring dormant D2.0R lesions with an LRH-1 inverse agonist resulted in sooner recurrence and metastatic outgrowth compared to vehicle treated mice. In summary, our findings suggest that LRH-1 plays a crucial role in regulating various neutrophil functions, including migration, NETosis, phagocytosis, and T cell expansion. The ultimate consequence of these regulations are control of dormant mammary cancer lesions. These results highlight LRH-1 as a potential therapeutic target for cancer treatment or prevention of metastatic recurrence. Funding: National Cancer Institute (ERN: R01CA234025) Department of Defense (ERN: BCRP Era of Hope Award) Citation Format: Yu Wang, Bryan Duong, Natalia Krawczynska, Shruti V. Bendre, Claire P. Schane, Erin Weisser, Lara Kockaya, Yifan Fei, Anasuya Das Gupta, Hashni E. Vidana Gamage, Adam T. Nelczyk, Dhanya Pradeep, Erik R. Nelson. The role of Liver Receptor Homolog 1 (LRH-1) in regulating cancer progression by modulating the immune response [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor-body Interactions: The Roles of Micro- and Macroenvironment in Cancer; 2024 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(22_Suppl):Abstract nr C027.

In-Depth Proteome Profiling of the Hippocampus of LDLR Knockout Mice Reveals Alternation in Synaptic Signaling Pathway.

The low-density lipoprotein receptor (LDLR) is a major apolipoprotein receptor that regulates cholesterol homeostasis. LDLR deficiency is associated with cognitive impairment by the induction of synaptopathy in the hippocampus. Despite the close relationship between LDLR and neurodegenerative disorders, proteomics research for protein profiling in the LDLR knockout (KO) model remains insufficient. Therefore, understanding LDLR KO-mediated differential protein expression within the hippocampus is crucial for elucidating a role of LDLR in neurodegenerative disorders. In this study, we conducted first-time proteomic profiling of hippocampus tissue from LDLR KO mice using tandem mass tag (TMT)-based MS analysis. LDLR deficiency induces changes in proteins associated with the transport of diverse molecules, and activity of kinase and catalyst within the hippocampus. Additionally, significant alterations in the expression of components in the major synaptic pathways were found. Furthermore, these synaptic effects were verified using a data-independent acquisition (DIA)-based proteomic method. Our data will serve as a valuable resource for further studies to discover the molecular function of LDLR in neurodegenerative disorders.

Liver X and thyroid hormone receptors in neurodegeneration

The role of thyroid hormone (TH) in the development and function of the central nervous system (CNS) has been known for many years. However, the role of liver X receptors (LXRs) in TH function and protection against neuronal degeneration was not recognized until recently. The relationship between thyroid hormone receptors (TRs) and LXRs became apparent with the cloning of steroid hormone receptors, leading to the discovery of the nuclear receptor superfamily. This family includes not only receptors for classical steroid hormones but also many newly discovered ligand-activated nuclear receptors. LXRs and TRs regulate overlapping pathways in lipid and carbohydrate metabolism, as well as in overall CNS development and function. These CNS pathways include neuronal migration during cortical and cerebellar layering, myelination, oligodendrocyte maturation, microglial activation, and astrocyte functions. Furthermore, LXRs likely have unique functions, as evidenced by the inability of TH to compensate for microglial activation, oligodendrocyte maturation, spinal motor neuron death, and degeneration of retinal and cochlear neurons in LXRβ knockout mice. The common and unique functions of these two receptors are the subject of this review. We analyzed some of the most relevant literature on the regulation and function of LXRs and TRs and investigated why both receptors are required in the human body. We conclude that LXRs and TRs do not represent parallel pathways but rather constitute a single pathway through which the TH endocrine system regulates cholesterol homeostasis. Subsequently, LXRs, activated by cholesterol metabolites, function as a paracrine/autocrine system that modulates the target cell response to TH.

ACAT1/SOAT1 maintains adipogenic ability in preadipocytes by regulating cholesterol homeostasis

Maintaining cholesterol homeostasis is critical for preserving adipocyte function during the progression of obesity. Despite this, the regulatory role of cholesterol esterification in governing adipocyte expandability has been understudied. Acyl-coenzyme A (CoA):cholesterol acyltransferase / Sterol O-acyltransferase 1 (ACAT1/SOAT1) is the dominant enzyme to synthesize cholesteryl ester in most tissues. Our previous study demonstrated that knockdown of either ACAT1 or ACAT2 impaired adipogenesis. However, the underlying mechanism of how ACAT1 mediates adipogenesis remains unclear. Here, we reported that ACAT1 is the dominant isoform in white adipose tissue of both humans and mice and knocking out ACAT1 reduced fat mass in mice. Furthermore, ACAT1-deficiency inhibited the early stage of adipogenesis via attenuating PPARγ pathway. Mechanistically, ACAT1 deficiency inhibited SREBP2-mediated cholesterol uptake and thus reduced intracellular and plasma membrane cholesterol level during adipogenesis. While replenishing cholesterol could rescue adipogenic master gene – Pparγ’s transcription in ACAT1 deficient cells during adipogenesis. Finally, overexpression of catalytically functional ACAT1, not the catalytic-dead ACAT1, rescued cholesterol level and efficiently rescued the transcription of PPARγ, as well as the adipogenesis in ACAT1-deficient preadipocytes. In summary, our study revealed the indispensable role of ACAT1 in adipogenesis via regulating intracellular cholesterol homeostasis.

KaiXinSan improves learning and memory impairment by regulating cholesterol homeostasis in mice overloaded with 27-OHC

Cholesterol and its oxidative products—oxysterols homeostasis— play a crucial role in maintaining cognitive function. Chinese medicine KaiXinSan (KXS) has demonstrated effectiveness in treating mental illness and regulating cognitive dysfunction of Alzheimer's disease (AD). The purpose of this article is to explore whether the KXS can enhance cognitive function by regulating cholesterol homeostasis. Employing the 27-hydroxy cholesterol (27-OHC) induced mice model of cognitive dysfunction and coculture model of assessment neurocyte damage, we investigated learning and memory abilities while concurrently addressing the reduction of neuronal cell damage through the regulation of cholesterol metabolism. 21 days of KXS treatment improved the learning and memory ability in mice 27-OHC-overloading by alleviating the exacerbated deposition of amyloid-β (Aβ), reducing inflammatory reactions, and mitigating synaptic plasticity damage. Additionally, it repaired myelin sheath function. More importantly, KXS significantly affects the metabolism of central cholesterol by substantially inhibiting the expression of liver X receptor (LXR), ATP-binding cassette transporter (ABCA1, ABCG1), apolipoprotein E (ApoE) and upregulated cytochrome P450 46A1(CYP46A1). Furthermore, KXS may alleviate 27-OHC-induced neuronal inflammation and apoptosis by promoting the conversion of cholesterol to 24-hydroxycholesterol (24-OHC) via CYP46A1 and suppressing cholesterol release from astrocyte cells. Altogether, our results demonstrate that KXS can prevent learning and memory impairments induced by 27-OHC loading. This effect may be related to its multitarget capability in promoting the conversion of excessive cholesterol to 24-OHC and maintaining a balance in cholesterol homeostasis and metabolism between neurons and astrocyte cells.

Inhibiting miRNA-146a suppresses mouse gallstone formation by regulating LXR/megalin/cubilin-media cholesterol absorption

BackgroundmiRNA has been implicated in regulating cholesterol homeostasis, a critical factor in gallstone formation. Here, we focused on elucidating the role of miR-146a in this pathological process. MethodsC57BL/6 mice were fed with lithogenic diet (LD) and injected with miR-146 antagomir (anta-146) via the tail vein for various weeks. The gallbladders and liver tissues were collected for cholesterol crystal imaging, gallstone mass quantification, and molecular analysis. Levels of cholesterol, bile salt, phospholipids, and metabolic parameters in serum and bile were assessed by ELISA. A 3′ UTR reporter gene assay was used to verify the direct target genes for miR-146. The relative expression of metabolism genes was analyzed by quantitative real-time PCR and immunoblotting. ResultsmiR-146a-5p expression was reduced in mice and clinical samples with gallstones. Anta-146 treatment effectively prevented LD-induced gallstone formation in mice without hepatic and cholecystic damage. The mice treated with anta-146 exhibited beneficial alterations in bile cholesterol and bile acids and lipid levels in the blood. A key biliary cholesterol transporter-Megalin was identified as a direct target of miR-146. Anta-146 administration upregulated megalin expression, thereby ameliorating impaired gallbladder cholesterol absorption associated with the LXR-megalin/cubilin pathway. ConclusionThe data demonstrates that miR-146 modulates gallbladder cholesterol absorption by targeting megalin, and prevents the pathogenesis of cholesterol gallstones.

Cannabidiol (CBD) Inhibits Foam Cell Formation via Regulating Cholesterol Homeostasis and Lipid Metabolism.

The cannabidiol (CBD) in hemp oil has important pharmacological activities. Accumulating evidence suggests that CBD is beneficial in the cardiovascular system and has been applied as a health supplement for atherosclerosis. However, the mechanism remains unclear. This study investigates the impact of CBD on foam cell formation, cholesterol homeostasis, and lipid metabolism in macrophages. CBD elevates the levels of peroxisome proliferator-activated receptor gamma (PPARγ) and its associated targets, such as ATP binding transporter A1/G1 (ABCA1/ABCG1), thus reducing foam cell formation, and increasing cholesterol efflux within macrophages. Notably, the upregulation of ABCA1 and ABCG1 expression induced by CBD is found to be attenuated by both a PPARγ inhibitor and PPARγ small interfering RNA (siRNA). Moreover, transfection of PPARγ siRNA results in a decrease in the inhibitory effect of CBD on foam cell formation and promotion of cholesterol efflux. Through lipidomics analysis, the study finds that CBD significantly reverses the enhancement of ceramide (Cer). Correlation analysis indicates a negative association between Cer level and the expression of ABCA1/ABCG1. This study confirms that CBD can be an effective therapeutic candidate for atherosclerosis treatment by activating PPARγ, up-regulating ABCA1/ABCG1 expression, and down-regulating Cer level.

Cholesin and GPR146 in Modulating Cholesterol Biosynthesis.

Cholesterol homeostasis in the human body is a crucial process that involves a delicate balance between dietary cholesterol absorption in the intestine and de novo cholesterol synthesis in the liver. Both pathways contribute significantly to the overall pool of cholesterol in the body, influencing plasma cholesterol levels and impacting cardiovascular health. Elevated absorption of cholesterol in the intestines has a suppressive impact on the synthesis of cholesterol in the liver, serving to preserve cholesterol balance. Nonetheless, the precise mechanisms driving this phenomenon remain largely unclear. This review aimed to discuss the previously unrecognized role of cholesin and GPR146 in the regulation of cholesterol biosynthesis, providing a novel conceptual framework for understanding cholesterol homeostasis. The discovery of cholesin, a novel protein implicated in the regulation of cholesterol homeostasis, represents a significant advancement in our understanding of cholesterol biosynthesis and its associated pathways. The cholesin-GPR146 axis could have profound implications across various therapeutic areas concerning abnormal cholesterol metabolism, offering new hope for patients and improving overall healthcare outcomes.

27-Hydroxycholesterol acts on estrogen receptor α expressed by POMC neurons in the arcuate nucleus to modulate feeding behavior.

Oxysterols are metabolites of cholesterol that regulate cholesterol homeostasis. Among these, the most abundant oxysterol is 27-hydroxycholesterol (27HC), which can cross the blood-brain barrier. Because 27HC functions as an endogenous selective estrogen receptor modulator, we hypothesize that 27HC binds to the estrogen receptor α (ERα) in the brain to regulate energy balance. Supporting this view, we found that delivering 27HC to the brain reduced food intake and activated proopiomelanocortin (POMC) neurons in the arcuate nucleus of the hypothalamus (POMCARH) in an ERα-dependent manner. In addition, we observed that inhibiting brain ERα, deleting ERα in POMC neurons, or chemogenetic inhibition of POMCARH neurons blocked the anorexigenic effects of 27HC. Mechanistically, we further revealed that 27HC stimulates POMCARH neurons by inhibiting the small conductance of the calcium-activated potassium (SK) channel. Together, our findings suggest that 27HC, through its interaction with ERα and modulation of the SK channel, inhibits food intake as a negative feedback mechanism against a surge in circulating cholesterol.

Methyl-CpG-binding protein 2 regulates CYP27A1-induced myometrial contraction during preterm labor.

Persistent and intense uterine contraction is a risk factor for preterm labor. We previously found that methyl-CpG-binding protein 2 (MeCP2), as a target of infection-related microRNA miR-212-3p, may play an inhibitory role in regulating myometrium contraction. However, the molecular mechanisms by which MeCP2 regulates myometrial contraction are still unknown. In this study, we found that MeCP2 protein expression was lower in myometrial specimens obtained from preterm labor cases, compared to those obtained from term labor cases. Herein, using RNA sequence analysis of global gene expression in human uterine smooth muscle cells (HUSMCs) following siMeCP2, we show that MeCP2 silencing caused dysregulation of the cholesterol metabolism pathway. Notably, MeCP2 silencing resulted in the upregulation of CYP27A1, the key enzyme involved in regulating cholesterol homeostasis, in HUSMCs. Methylation-specific PCR, chromatin immunoprecipitation, and dual luciferase reporter gene technology indicated that MeCP2 could bind to the methylated CYP27A1 promoter region and repress its transcription. Administration of siCYP27A1 in a lipopolysaccharide (LPS)-induced preterm labor mouse model delayed the onset of preterm labor. Human preterm myometrium and the LPS-induced preterm labor mouse model both showed lower expression of MeCP2 and increased expression of CYP27A1. These results demonstrated that aberrant upregulation of CYP27A1 induced by MeCP2 silencing is one of the mechanisms facilitating inappropriate myometrial contraction. CYP27A1 could be exploited as a novel therapeutic target for preterm birth.

Membrane specificity of the human cholesterol transfer protein STARD4

STARD4 regulates cholesterol homeostasis by transferring cholesterol between the plasma membrane and endoplasmic reticulum. The STARD4 structure features a helix-grip fold surrounding a large hydrophobic cavity holding the sterol. Its access is controlled by a gate formed by the Ω1 and Ω4 loops and the C-terminal α-helix. Little is known about the mechanisms by which STARD4 binds to membranes and extracts/releases cholesterol. All available structures of STARD4 are without a bound sterol and display the same closed conformation of the gate. The cholesterol transfer activity of the mouse STARD4 is enhanced in the presence of anionic lipids, and in particular of phosphatidylinositol biphosphates (PIP2) for which two binding sites were proposed on the mouse STARD4 surface. Yet only one of these sites is conserved in human STARD4. We here report the results of a liposome microarray-based assay and microseconds-long molecular dynamics simulations of human STARD4 with complex lipid bilayers mimicking the composition of the donor and acceptor membranes. We show that the binding of apo form of human STARD4 is sensitive to the presence of PIP2 through two specific binding sites, one of which was not identified on mouse STARD4. We report two novel conformations of the gate in holo-STARD4: a yet-unobserved close conformation and an open conformation of Ω4 shedding light on the opening/closure mechanism needed for cholesterol uptake/release. Overall, the modulation of human STARD4 membrane-binding by lipid composition, and by the presence of the cargo supports the capacity of human STARD4 to achieve directed transfer between specific organelle membranes.

Circulating microRNA-33b levels are associated with the presence and severity of coronary heart disease

MicroRNA-33b (miR-33b) affected various biological pathways in regulating cholesterol homeostasis which may link to the pathogenesis of atherosclerotic lesions. However, whether this marker is associated with the presence and severity of coronary heart disease (CHD) is undetermined. We aim to explore the diagnostic value of circulating miR-33b level in the presence and severity of CHD. Altogether 320 patients were enrolled, including 240 patients diagnosed with CHD while 80 were classified as controls after CAG examination. Circulating miR-33b level was analyzed in all subjects, the Gensini score was calculated to assess the severity of stenotic lesions. The association between miR-33b and the presence and severity of CHD was analyzed, and the diagnostic potential of miR-33b of CHD was performed by the receiver operating characteristic (ROC) analysis. The CHD group had higher miR-33b levels (p < 0.001), and the miR-33b content significantly elevated following an increasing Gensini score (p for trend < 0.001). After adjustments for potential risk factors, such as several blood lipid markers, miR-33b remained a significant determinant for CHD (p < 0.001). ROC analysis disclosed that the AUC was 0.931. The optimal cutoff value of miR-33b was with a sensitivity of 81.3% and a specificity of 98.7% in differentiating CHD. It can prognosticate that the higher level of miR-33b was linked to increased severity of disease in CHD patients. Thus, the application of this marker might assist in the diagnosis and classification of CHD patients. Nevertheless, additional studies with larger sample sizes will be required to verify these results.

Specific circulating miRNAs are associated with plasma lipids in a healthy American cohort.

Low-density lipoprotein cholesterol (LDL-c) is both a therapeutic target and a risk factor for cardiovascular disease (CVD). MicroRNA (miRNA) has been shown to regulate cholesterol homeostasis, and miRNA in blood circulation has been linked to hypercholesterolemia. However, few studies to date have associated miRNA with phenotypes like LDL-c in a healthy population. To this end, we analyzed circulating miRNA in relation to LDL-c in a healthy cohort of 353 participants using two separate bioinformatic approaches. The first approach found that miR-15b-5p and miR-16-5p were upregulated in individuals with at-risk levels of LDL-c. The second approach identified two miRNA clusters, one that positively and a second that negatively correlated with LDL-c. Included in the cluster that positively correlated with LDL-c were miR-15b-5p and miR-16-5p, as well as other miRNA from the miR-15/107, miR-30, and let-7 families. Cross-species analyses suggested that several miRNAs that associated with LDL-c are conserved between mice and humans. Finally, we examined the influence of diet on circulating miRNA. Our results robustly linked circulating miRNA with LDL-c, suggesting that miRNA could be used as biomarkers for hypercholesterolemia or targets for developing cholesterol-lowering drugs.NEW & NOTEWORTHY This study explored the association between circulating microRNA (miRNA) and low-density lipoprotein cholesterol (LDL-c) in a healthy population of 353 participants. Two miRNAs, miR-15b-5p and miR-16-5p, were upregulated in individuals with at-risk LDL-c levels. Several miRNA clusters were positively and negatively correlated with LDL-c and are known to target mRNA involved in lipid metabolism. The study also investigated the influence of diet on circulating miRNA, suggesting potential biomarkers for hypercholesterolemia.

Role of ABCA1 in Atherosclerosis: Novel Mutations and Potential Plant-derived Therapies.

ATP-binding cassette transporter A1 (ABCA1) is one of the key proteins regulating cholesterol homeostasis and playing a crucial role in atherosclerosis development. ABCA1 regulates the rate-limiting step of reverse cholesterol transport, facilitates the efflux of surplus intracellular cholesterol and phospholipids, and suppresses inflammation through several signalling pathways. At the same time, many mutations and Single Nucleotide Polymorphisms (SNPs) have been identified in the ABCA1 gene, which affects its biological function and is associated with several hereditary diseases (such as familial hypo-alpha-lipoproteinaemia and Tangier disease) and increased risk of cardiovascular diseases (CVDs). This review summarises recently identified mutations and SNPs in their connection to atherosclerosis and associated CVDs. Also, we discuss the recently described application of various plant-derived compounds to modulate ABCA1 expression in different in vitro and in vivo models. Herein, we present a comprehensive overview of the association of ABCA1 mutations and SNPs with CVDs and as a pharmacological target for different natural-derived compounds and highlight the potential application of these phytochemicals for treating atherosclerosis through modulation of ABCA1 expression.

Abstract 632: AKT supports cancer cell survival through modulation of cholesterol homeostasis

Abstract AKT is a critical effector kinase downstream of PI3K activation. It has been shown to regulate a variety of cellular processes important for homeostasis, many of which are altered during oncogenesis. Not surprisingly, AKT is constitutively activated in a large number of human cancers, and has consequently been pursued as a therapeutic target for many years. Some of these functions are directly involved in establishing one or more hallmarks of cancer including sustained proliferative signaling, resisting cell death, and reprogrammed cellular metabolism. Although AKT inhibitors have demonstrated clinical benefit (most recently in a phase III trial) in combination with other therapies, single agent activity has been limited to a few cases with relatively infrequent activating AKT1 mutations. We have previously proposed that the clear disconnect between the high frequency of AKT activation in cancer and the lack of broad clinical activity of AKT inhibitors is due, at least in part, to the inability of existing compounds to block non-catalytic functions. We have found that while allosteric AKT inhibitors are partial suppressors of these functions, ATP-competitive inhibitors fail to suppress these functions to any significant extent. We now provide evidence that one important non-catalytic function of AKT that impinges on its oncogenic function is the regulation of cholesterol metabolism. We show that AKT represses the activation of LXRβ, thereby maintaining a level of intracellular cholesterol that is compatible with cancer cell viability, and that this repression does not require catalytic activity. Consistently, we find that allosteric AKT inhibitors induce LXRβ activation, and that genetic or pharmacological suppression of LXRβ function limit the growth inhibiting effects of these drugs. Our findings suggest that through a kinase-independent activity, AKT may play a significant role in the regulation of cholesterol homeostasis, and that the therapeutic potential of AKT inhibitors could be broaden by optimizing their ability to interfere with these functions. Citation Format: Igor Vivanco, Khine N. Myint, Sean Wallace, Glorianne Lazaro, Eleftherios Kostaras, Nikolaos Palaskas. AKT supports cancer cell survival through modulation of cholesterol homeostasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 632.

NOVA1 acts as an oncogenic RNA-binding protein to regulate cholesterol homeostasis in human glioblastoma cells

NOVA1 is a neuronal RNA-binding protein identified as the target antigen of a rare autoimmune disorder associated with cancer and neurological symptoms, termed paraneoplastic opsoclonus-myoclonus ataxia. Despite the strong association between NOVA1 and cancer, it has been unclear how NOVA1 function might contribute to cancer biology. In this study, we find that NOVA1 acts as an oncogenic factor in a GBM (glioblastoma multiforme) cell line established from a patient. Interestingly, NOVA1 and Argonaute (AGO) CLIP identified common 3' untranslated region (UTR) targets, which were down-regulated in NOVA1 knockdown GBM cells, indicating a transcriptome-wide intersection of NOVA1 and AGO-microRNA (miRNA) targets regulation. NOVA1 binding to 3'UTR targets stabilized transcripts including those encoding cholesterol homeostasis related proteins. Selective inhibition of NOVA1-RNA interactions with antisense oligonucleotides disrupted GBM cancer cell fitness. The precision of our GBM CLIP studies point to both mechanism and precise RNA sequence sites to selectively inhibit oncogenic NOVA1-RNA interactions. Taken together, we find that NOVA1 is commonly overexpressed in GBM, where it can antagonize AGO2-miRNA actions and consequently up-regulates cholesterol synthesis, promoting cell viability.

Antagonism of let-7c reduces atherosclerosis and macrophage lipid accumulation by promoting PGC-1α/LXRα/ABCA1/G1 pathway

Changes in circulating let-7c were significantly associated with the alter in lipid profile, but its role in intracellular lipid metabolism remains unknown. This work was conducted to explore the effects of let-7c on the lipid accumulation in macrophages and uncover the underlying mechanism. Our results showed that let-7c inhibition relieved atherosclerosis progression in apoE-/- mice. In ox-LDL-treatment macrophages, let-7c knockdown suppressed lipid accumulation but does no affect cholesterol intake. Consistent with this, overexpression of let-7c promoted lipid accumulation by reducing the expression of LXRα and ABCA1/G1. Mechanistically, let-7c targeted PGC-1α to repress the expression of LXRα and ABCA1/G1, thereby regulating cholesterol homeostasis in macrophages. Taken together, these findings suggest that antagonism of let-7c reduces atherosclerosis and macrophage lipid accumulation through the PGC-1α/LXRα/ABCA1/G1 axis.

Evidence for hypoxia-induced dysregulated cholesterol homeostasis in preeclampsia: Insights into the mechanisms from human placental cells and tissues.

Preeclampsia (PE) poses a considerable risk to the long-term cardiovascular health of both mothers and their offspring due to a hypoxic environment in the placenta leading to reduced fetal oxygen supply. Cholesterol is vital for fetal development by influencing placental function. Recent findings suggest an association between hypoxia, disturbed cholesterol homeostasis, and PE. This study investigates the influence of hypoxia on placental cholesterol homeostasis. Using primary human trophoblast cells and placentae from women with PE, various aspects of cholesterol homeostasis were examined under hypoxic and hypoxia/reoxygenation (H/R) conditions. Under hypoxia and H/R, intracellular total and non-esterified cholesterol levels were significantly increased. This coincided with an upregulation of HMG-CoA-reductase and HMG-CoA-synthase (key genes regulating cholesterol biosynthesis), and a decrease in acetyl-CoA-acetyltransferase-1 (ACAT1), which mediates cholesterol esterification. Hypoxia and H/R also increased the intracellular levels of reactive oxygen species and elevated the expression of hypoxia-inducible factor (HIF)-2α and sterol-regulatory-element-binding-protein (SREBP) transcription factors. Additionally, exposure of trophoblasts to hypoxia and H/R resulted in enhanced cholesterol efflux to maternal and fetal serum. This was accompanied by an increased expression of proteins involved in cholesterol transport such as the scavenger receptor class B type I (SR-BI) and the ATP-binding cassette transporter G1 (ABCG1). Despite these metabolic alterations, mitogen-activated-protein-kinase (MAPK) signaling, a key regulator of cholesterol homeostasis, was largely unaffected. Our findings indicate dysregulation of cholesterol homeostasis at multiple metabolic points in both the trophoblast hypoxia model and placentae from women with PE. The increased cholesterol efflux and intracellular accumulation of non-esterified cholesterol may have critical implications for both the mother and the fetus during pregnancy, potentially contributing to an elevated cardiovascular risk later in life.

The supplementation of a high dose of fish oil during pregnancy and lactation led to an elevation in Mfsd2a expression without any changes in docosahexaenoic acid levels in the retina of healthy 2-month-old mouse offspring.

During fetal development, the proper development of neural and visual systems relies on the maternal supplementation of omega-3 fatty acids through placental transfer. Pregnant women are strongly advised to augment their diet with additional sources of omega-3, such as fish oil (FO). This supplementation has been linked to a reduced risk of preterm birth, pre-eclampsia, and perinatal depression. Recently, higher doses of omega-3 supplementation have been recommended for pregnant women. Considering that omega-3 fatty acids, particularly docosahexaenoic acid (DHA), play a crucial role in maintaining the delicate homeostasis required for the proper functioning of the retina and photoreceptors the effects of high-dose fish oil (FO) supplementation during pregnancy and lactation on the retina and retinal pigmented epithelium (RPE) in healthy offspring warrant better understanding. The fatty acid content and the changes in the expression of the genes regulating cholesterol homeostasis and DHA transport in the retina and RPE were evaluated following the high-dose FO supplementation. Our study demonstrated that despite the high-dose FO treatment during pregnancy and lactation, the rigorous DHA homeostasis in the retina and RPE of the two-month-old offspring remained balanced. Another significant finding of this study is the increase in the expression levels of major facilitator superfamily domain-containing protein (Mfsd2a), a primary DHA transporter. Mfsd2a also serves as a major regulator of transcytosis during development, and a reduction in Mfsd2a levels poses a major risk for the development of leaky blood vessels. Impairment of the blood-retinal barrier (BRB) is associated with the development of numerous ocular diseases, and a better understanding of how to manipulate transcytosis in the BRB during development can enhance drug delivery through the BRB or contribute to the repair of central nervous system (CNS) barriers.