Intracellular Cholesterol Metabolism Research Articles

25-Hydroxycholesterol attenuates tumor necrosis factor alpha-induced blood-brain barrier breakdown in vitro

Intracellular cholesterol metabolism is regulated by the SREBP-2 and LXR signaling pathways. The effects of inflammation on these molecular mechanisms remain poorly studied, especially at the blood-brain barrier (BBB) level. Tumor necrosis factor α (TNFα) is a proinflammatory cytokine associated with BBB dysfunction. Therefore, the aim of our study was to investigate the effects of TNFα on BBB cholesterol metabolism, focusing on its underlying signaling pathways. Using a human in vitro BBB model composed of human brain-like endothelial cells (hBLECs) and brain pericytes (HBPs), we observed that TNFα increases BBB permeability by degrading the tight junction protein CLAUDIN-5 and activating stress signaling pathways in both cell types. TNFα also promotes cholesterol release and decreases cholesterol accumulation and APOE secretion. In hBLECs, the expression of SREBP-2 targets (LDLR and HMGCR) is increased, while ABCA1 expression is decreased. In HBPs, only LDLR and ABCA1 expression is increased. TNFα treatment also induces 25-hydroxycholesterol (25-HC) production, a cholesterol metabolite involved in the immune response and intracellular cholesterol metabolism. 25-HC pretreatment attenuates TNFα-induced BBB leakage and partially alleviates the effects of TNFα on ABCA1, LDLR, and HMGCR expression. Overall, our results suggest that TNFα favors cholesterol efflux via an LXR/ABCA1-independent mechanism at the BBB, while it activates the SREBP-2 pathway. Treatment with 25-HC partially reversed the effect of TNFα on the LXR/SREBP-2 pathways. Our study provides novel perspectives for better understanding cerebrovascular signaling events linked to BBB dysfunction and cholesterol metabolism in neuroinflammatory diseases.

AGFG1 increases cholesterol biosynthesis by disrupting intracellular cholesterol homeostasis to promote PDAC progression

PurposeCholesterol metabolism reprograming has been acknowledged as a novel feature of cancers. Pancreatic ductal adenocarcinoma (PDAC) is a cancer with a high demand of cholesterol for rapid growth. The underlying mechanism of how cholesterol metabolism homestasis are disturbed in PDAC is explored. Experimental designThe relevance between PDAC and cholesterol was confirmed in TCGA database. The expression and clinical association were discovered in TCGA and GEO datasets. Knockdown and overexpression of AGFG1 was adopted to perform function studies. RNA sequencing, cholesterol detection, transmission electron microscope, co-immunoprecipitation, and immunofluorescence et al. were utilized to reveal the underlying mechanism. ResultsAGFG1 was identified as one gene positively correlated with cholesterol metabolism in PDAC as revealed by bioinformatics analysis. AGFG1 expression was then found associated with poor prognosis in PDAC. AGFG1 knockdown led to decreased proliferation of tumor cells both in vitro and in vivo. By RNA sequencing, we found AGFG1 upregulated expression leads to enhanced intracellular cholesterol biosynthesis. AGFG1 knockdown suppressed cholesterol biosynthesis and an accumulation of cholesterol in the ER. Mechanistically, we confirmed that AGFG1 interacted with CAV1 to relocate cholesterol for the proceeding of cholesterol biosynthesis, therefore causing disorders in intracellular cholesterol metabolism. ConclusionsOur study demonstrates the tumor-promoting role of AGFG1 by disturbing cholesterol metabolism homestasis in PDAC. Our study has present a new perspective on cancer therapeutic approach based on cholerstrol metabolism in PDAC.

Loss of Sc5d results in micrognathia due to a failure in osteoblast differentiation

IntroductionMutations in genes related to cholesterol metabolism, or maternal diet and health status, affect craniofacial bone formation. However, the precise role of intracellular cholesterol metabolism in craniofacial bone development remains unclear. ObjectiveThe aim of this study is to determine how cholesterol metabolism aberrations affect craniofacial bone development. MethodsMice with a deficiency in Sc5d, which encodes an enzyme involved in cholesterol synthesis, were analyzed with histology, micro computed tomography (microCT), and cellular and molecular biological methods. ResultsSc5d null mice exhibited mandible hypoplasia resulting from defects in osteoblast differentiation. The activation of the hedgehog and WNT/β-catenin signaling pathways, which induce expression of osteogenic genes Col1a1 and Spp1, was compromised in the mandible of Sc5d null mice due to a failure in the formation of the primary cilium, a cell surface structure that senses extracellular cues. Treatments with an inducer of hedgehog or WNT/β-catenin signaling or with simvastatin, a drug that restores abnormal cholesterol production, partially rescued the defects in osteoblast differentiation seen in Sc5d mutant cells. ConclusionOur results indicate that loss of Sc5d results in mandibular hypoplasia through defective primary cilia-mediated hedgehog and WNT/β-catenin signaling pathways.

Abstract 6486: Single nucleotide polymorphisms that predict serum cholesterol as a prostate cancer prognostic factor - a Mendelian randomization study

Abstract Introduction: Intracellular cholesterol metabolism plays an important role in prostate cancer progression and emergence of treatment resistance. However, it remains unclear whether serum cholesterol and lipoproteins are associated with prostate cancer outcomes. Studies on serum cholesterol and cancer are often confounded by lifestyle factors such as diet and obesity. A possible solution is to use instrumental variables, such as SNPs predicting serum cholesterol. According to the Mendelian randomization theory, germline SNP distribution is unaffected by confounding variables such as diet and lifestyle factors. Objective: To estimate whether SNPs that predict serum cholesterol and lipoproteins also predict mortality among a cohort of men with prostate cancer. Methods: Our study cohort consisted of 3,241 men diagnosed with prostate cancer between 1996-2015, using data collected by the Finnish Randomized Study of Screening for Prostate Cancer. Blood samples were genotyped by PRACTICAL consortium. A UCSC genome browser was utilized for selecting 85 SNPs in lipid metabolism-associated genes. Dates and causes of deaths between 1996-2015 were obtained from the Statistics Finland's statistics on causes of death. Information on serum cholesterol and lipoprotein measurements were obtained from a regional laboratory database.Scores predicting serum cholesterol, LDL, HDL and triglyceride level by SNP genotype were created using linear regression and lasso regression. Risk of prostate cancer death and overall mortality by level of the SNP risk score were evaluated with multivariable-adjusted Cox regression. Follow-up started at prostate cancer diagnosis and continued until death, emigration or common closing date of Dec 31, 2015.Results: SNP score predicting total cholesterol stratified prostate cancer patients both for disease-specific (HR 1.27, 95% CI 0.49-3.28 for highest tertile vs. lowest) and overall survival (HR 1.43, 95% CI 0.94-2.20, p for trend = 0.077), albeit statistical significance was not reached. Similar survival differences were observed for SNP score predicting triglyceride level, but not for scores predicting LDL or HDL.Conclusions: SNPs predicting serum cholesterol and triglycerides are likely prognostic factors for survival of prostate cancer patients. This suggest serum cholesterol and lipoproteins areimportant in prostate cancer progression. Total cholesterol SNP scoreProstate-cancer specific survival Overall survival Citation Format: Sebastian Boele, Aino Siltari, Paavo Raittinen, Johanna Schleutker, Kimmo Taari, Kirsi Talala, Teuvo Tammela, Anssi Auvinen, Teemu J. Murtola. Single nucleotide polymorphisms that predict serum cholesterol as a prostate cancer prognostic factor - a Mendelian randomization study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6486.

ERRα Up-Regulates Invadopodia Formation by Targeting HMGCS1 to Promote Endometrial Cancer Invasion and Metastasis.

Estrogen-related receptor alpha (ERRα) plays an important role in endometrial cancer (EC) progression. However, the biological roles of ERRα in EC invasion and metastasis are not clear. This study aimed to investigate the role of ERRα and 3-hydroxy-3-methylglutaryl-CoA synthase 1 (HMGCS1) in regulating intracellular cholesterol metabolism to promote EC progression. ERRα and HMGCS1 interactions were detected by co-immunoprecipitation, and the effects of ERRα/HMGCS1 on the metastasis of EC were investigated by wound-healing and transwell chamber invasion assays. Cellular cholesterol content was measured to verify the relationship between ERRα and cellular cholesterol metabolism. Additionally, immunohistochemistry was performed to confirm that ERRα and HMGCS1 were related to EC progression. Furthermore, the mechanism was investigated using loss-of-function and gain-of-function assays or treatment with simvastatin. High expression levels of ERRα and HMGCS1 promoted intracellular cholesterol metabolism for invadopodia formation. Moreover, inhibiting ERRα and HMGCS1 expression significantly weakened the malignant progression of EC in vitro and in vivo. Our functional analysis showed that ERRα promoted EC invasion and metastasis through the HMGCS1-mediated intracellular cholesterol metabolism pathway, which was dependent on the epithelial-mesenchymal transition pathway. Our findings suggest that ERRα and HMGCS1 are potential targets to suppress EC progression.

Redox integration of signaling and metabolism in a head and neck cancer model of radiation resistance using COSMRO.

Redox metabolism is increasingly investigated in cancer as driving regulator of tumor progression, response to therapies and long-term patients' quality of life. Well-established cancer therapies, such as radiotherapy, either directly impact redox metabolism or have redox-dependent mechanisms of action defining their clinical efficacy. However, the ability to integrate redox information across signaling and metabolic networks to facilitate discovery and broader investigation of redox-regulated pathways in cancer remains a key unmet need limiting the advancement of new cancer therapies. To overcome this challenge, we developed a new constraint-based computational method (COSMro) and applied it to a Head and Neck Squamous Cell Cancer (HNSCC) model of radiation resistance. This novel integrative approach identified enhanced capacity for H2S production in radiation resistant cells and extracted a key relationship between intracellular redox state and cholesterol metabolism; experimental validation of this relationship highlights the importance of redox state in cellular metabolism and response to radiation.

PS-B04-8: YM750, AN ACAT1 INHIBITOR, REDUCES ALDOSTERONE SECRETION BY DECREASING ADRENAL CYP11B2 EXPRESSION

Primary aldosteronism (PA) is a refractory hypertension that accounts for approximately 5%-10% of hypertensive patients. aldosterone-producing adenomas and idiopathic hyperaldosteronism are known causes of PA. In aldosterone-producing adenomas, depolarization due to somatic mutations of ion channels in adrenocortical cells is considered the cause of aldosterone oversecretion. Recently, there have been reports on the expression of various cholesterol-metabolizing enzymes in aldosterone-producing adenomas, suggesting that intracellular cholesterol metabolism is very important for aldosterone secretion. We present here the possibility that an inhibitor of Acetyl-CoA acetyltransferase (ACAT1), an enzyme that converts cholesterol to cholesteryl esters, may inhibit aldosterone secretion by depolarization in adrenal cells. Potassium chloride and YM750, an ACAT1 inhibitor, were added to human adrenocortical carcinoma, H295R cells. Then, we measured aldosterone synthase gene, CYP11B2 mRNA expression level. As a result, the expression level of CYP11B2 decreased. Both NURR1 and NGFIB mRNA expression levels also decreased. Additionally, aldosterone production was also measured and found to be significantly decreased in the YM750 added group. Next, angiotensin II was added and the inhibitory effect of YM750 was examined. The results showed that CYP11B2 expression was not decreased. This indicates that YM750 decreased the induction of CYP11B2 expression in a potassium chloride-induced stimulus-specific manner. The experimental results suggest that YM750 specifically inhibits CYP11B2 gene expression by cell depolarization and suppresses aldosterone secretion. However, there are few reports of cholesterol metabolism affecting CYP11B2 gene expression. In this study, we found that intracellular cholesterol metabolism may affect CYP11B2 gene expression. We plan to investigate the relationship between ACAT inhibition and CYP11B2 gene expression in detail mechanisms in the future.

Phenotype-genotype correlation in aldosterone-producing adenomas characterized by intracellular cholesterol metabolism

Aldosterone-producing adenoma (APA) is histologically composed of clear and compact tumor cells. KCNJ5- mutated APAs were reported to be associated with higher plasma aldosterone concentration and more abundant clear tumor cells containing lipid droplets than non-KCNJ5- mutated APAs. However, the association among cholesterol uptake and/or synthesis, cellular morphology and genotypes has remained unknown. Therefore, in order to explore these differences, 52 APA cases (KCNJ5 mt: n = 33, non-KCNJ5 mt: n = 19; ATP1A1: n = 3, ATP2B3: n = 3, CACNA1D: n = 5, CTNNB1: n = 1, tumors without any mutation above: n = 7), zona glomerulosa (ZG) tissue adjacent to APA and 10 non-pathological adrenal glands (NAs) were examined for quantitative histopathological analysis of tumor morphology and immunohistochemical analysis of cholesterol receptors (SR-B1, LDL-R), cholesterol metabolic enzymes (ACAT1, ACAT2, HSL, DHCR24, StAR), and the enzymes required for steroid synthesis (CYP11A1, CYP17A, 3βHSD, CYP11B1, CYP11B2). Gas chromatography-mass spectrometry (GC-MS) analysis was further performed to profile cholesterol precursors and metabolites in 21 APA cases (KCNJ5 mt: n = 16, non-KCNJ5 mt: n = 5) and 14 adrenal cortex of adjacent adrenal tissues. Results demonstrated that both SR-B1 and DHCR24 were significantly lower in the ZG than in fasciculata or reticularis of NAs but LDL-R was not significantly different among them in immunohistochemical analysis. SR-B1 and DHCR24 were both significantly higher in APAs than in ZG tissue adjacent to APA. In GC-MS analysis, most cholesterol precursors and metabolites, except for lanosterol, and their metabolic ratios (= concentration of cholesterol/ precursor) were higher in APAs than in the adjacent adrenal cortex tissue. LDL-R, ACAT1/2, HSL, DHCR24 were all significantly lower in clear than in compact tumor cells of APA. LDL-R was significantly lower and cholesterol/lanosterol ratio was significantly higher in KCNJ5- mutated than non-KCNJ5- mutated APAs. We demonstrated SR-B1 mediated selective uptake of cholesterol ester and de novo cholesterol synthesis were both enhanced in APAs. In addition, cholesterol uptake and metabolism were different between clear and compact tumor cells. KCNJ5- mutated APAs were predominantly composed of clear tumor cells containing abundant cholesteryl ester but less activated LDL-R mediated uptake and increased de novo synthesis. Those findings above indicated their more pronounced functional deviation from the normal ZG cells in terms of their steroidogenic and intracellular cholesterol metabolism.

Ether Lipids in Obesity: From Cells to Population Studies.

Ether lipids are a unique class of glycero- and glycerophospho-lipid that carry an ether or vinyl ether linked fatty alcohol at the sn-1 position of the glycerol backbone. These specialised lipids are important endogenous anti-oxidants with additional roles in regulating membrane fluidity and dynamics, intracellular signalling, immunomodulation and cholesterol metabolism. Lipidomic profiling of human population cohorts has identified new associations between reduced circulatory plasmalogen levels, an abundant and biologically active sub-class of ether lipids, with obesity and body-mass index. These findings align with the growing body of work exploring novel roles for ether lipids within adipose tissue. In this regard, ether lipids have now been linked to facilitating lipid droplet formation, regulating thermogenesis and mediating beiging of white adipose tissue in early life. This review will assess recent findings in both population studies and studies using cell and animal models to delineate the functional and protective roles of ether lipids in the setting of obesity. We will also discuss the therapeutic potential of ether lipid supplementation to attenuate diet-induced obesity.

Prostate cancer cell proliferation is influenced by LDL-cholesterol availability and cholesteryl ester turnover

BackgroundProstate cancer growth is driven by androgen receptor signaling, and advanced disease is initially treatable by depleting circulating androgens. However, prostate cancer cells inevitably adapt, resulting in disease relapse with incurable castrate-resistant prostate cancer. Androgen deprivation therapy has many side effects, including hypercholesterolemia, and more aggressive and castrate-resistant prostate cancers typically feature cellular accumulation of cholesterol stored in the form of cholesteryl esters. As cholesterol is a key substrate for de novo steroidogenesis in prostate cells, this study hypothesized that castrate-resistant/advanced prostate cancer cell growth is influenced by the availability of extracellular, low-density lipoprotein (LDL)-derived, cholesterol, which is coupled to intracellular cholesteryl ester homeostasis.MethodsC4-2B and PC3 prostate cancer cells were cultured in media supplemented with fetal calf serum (FCS), charcoal-stripped FCS (CS-FCS), lipoprotein-deficient FCS (LPDS), or charcoal-stripped LPDS (CS-LPDS) and analyzed by a variety of biochemical techniques. Cell viability and proliferation were measured by MTT assay and Incucyte, respectively.ResultsReducing lipoprotein availability led to a reduction in cholesteryl ester levels and cell growth in C4-2B and PC3 cells, with concomitant reductions in PI3K/mTOR and p38MAPK signaling. This reduced growth in LPDS-containing media was fully recovered by supplementation of exogenous low-density lipoprotein (LDL), but LDL only partially rescued growth of cells cultured with CS-LPDS. This growth pattern was not associated with changes in androgen receptor signaling but rather increased p38MAPK and MEK1/ERK/MSK1 activation. The ability of LDL supplementation to rescue cell growth required cholesterol esterification as well as cholesteryl ester hydrolysis activity. Further, growth of cells cultured in low androgen levels (CS-FCS) was suppressed when cholesteryl ester hydrolysis was inhibited.ConclusionsOverall, these studies demonstrate that androgen-independent prostate cancer cell growth can be influenced by extracellular lipid levels and LDL-cholesterol availability and that uptake of extracellular cholesterol, through endocytosis of LDL-derived cholesterol and subsequent delivery and storage in the lipid droplet as cholesteryl esters, is required to support prostate cancer cell growth. This provides new insights into the relationship between extracellular cholesterol, intracellular cholesterol metabolism, and prostate cancer cell growth and the potential mechanisms linking hypercholesterolemia and more aggressive prostate cancer.

Insulin-induced genes INSIG1 and INSIG2 mediate oxysterol-dependent activation of the PERK–eIF2α–ATF4 axis

Insulin-induced genes (INSIGs) encode endoplasmic reticulum–resident proteins that regulate intracellular cholesterol metabolism. Oxysterols are oxygenated derivatives of cholesterol, some of which orchestrate lipid metabolism via interaction with INSIGs. Recently, it was reported that expression of activating transcription factor-4 (ATF4) was induced by certain oxysterols; the precise of mechanism is unclear. Herein, we show that INSIGs mediate ATF4 upregulation upon interaction with oxysterol. Oxysterols that possess a high affinity for INSIG, such as 27- and 25-hydroxycholesterol (25HC), markedly induced the increase of ATF4 protein when compared with other oxysterols. In addition, ATF4 upregulation by these oxysterols was attenuated in INSIG1/2-deficient Chinese hamster ovary cells and recovered by either INSIG1 or INSIG2 rescue. Mechanistic studies revealed that the binding of 25HC to INSIG is critical for increased ATF4 protein via activation of protein kinase RNA-activated–like ER kinase and eukaryotic translation initiation factor 2α. Knockout of INSIG1 or INSIG2 in human hepatoma Huh7 cells attenuated ATF4 protein upregulation, indicating that only one of the endogenous INSIGs, unlike overexpression of intrinsic INSIG1 or INSIG2, was insufficient for ATF4 induction. Furthermore, ATF4 proactively upregulated the cell death–inducible gene expression, such as Chop, Chac1, and Trb3, thereby markedly reducing cell viability with 25HC. These findings support a model whereby that INSIGs sense an increase in oxysterol in the endoplasmic reticulum and induce an increase of ATF4 protein via the protein kinase RNA-activated–like ER kinase–eukaryotic translation initiation factor 2α pathway, thereby promoting cell death.

Intracellular Cholesterol Metabolism in Aldosterone-Producing Adenoma.~A Possible Association With Cellular Morphometry and Genotype~

Introduction: Primary aldosteronism (PA) is the most common cause of secondary hypertension. More than 70% of APAs have been reported to have KCNJ5 somatic mutation in Asian countiries. Patients with KCNJ5 mutated APAs generally harbor high plasma aldosterone concentration (PAC), and are mainly composed of clear tumor cells containing abundant lipid droplets. However, an association among intracellular cholesterol metabolism, morphological features and genotypes in tumor cells has remained virtually unknown.[Materials and methods]Three cholesterol receptors (SR-B1, LDL-R, VLDL-R) were immunolocakized in 25 APA cases (KCNJ5 mt: n= 15, WT: n=10) who underwent adrenalectomy at Tohoku University Hospital. Image analysis software (HALO, India Labs) was used to quantitatively analyze the intracellular localization and immunoreactivity and expored their correlation with genotype and clinical factors.[Results]LDL-R immunoreactivity was significantly lower in KCNJ5 mt group than WT group (P = 0.0369). In KCNJ5 mt group, a significant correlation was detected between LDL-R immunoreactivity and CYP11B2 (Aldosterone synthase), (P = 0.0271, ρ = 0.5684) but not in WT group. In addition, LDL-R immunoreactivity was significantly inversely correlated with tumor size (P = 0.0142, ρ = -0.6176) and PAC (P = <0.001, ρ = -0.7179) in mt group as well as in whole APA cases.[Discussion]This is the first study to compare cholesterol receptor expression profiles with morphological tumor cell subtype, genotype, and clinical data in APAs. Results indicated that KCNJ5 mt APAabundantly stored cholesterol ester in their cytoplasm and cholesterol uptake was less activated, resulting In rather efficient aldosterone biosynthesis in tumor cells. In addition, a significant correlation was detected between LDL-R and CYP11B2 with the abundant localization of LDL-R in tumor cells. Therefore, LDL-R could be a predominant resource of plasma lipoprotein uptake in aldosterone-producing tumor cells, especially for KCNJ5mt APAs.

Impact of cholesterol-pathways on breast cancer development, a metabolic landscape.

ApoB-lipoproteins and their components modulate intracellular metabolism and have been associated with the development of neoplastic phenomena, such as proliferation, anchorage-independent growth, epithelial-mesenchymal transition, and cancer invasion. In cancer cells, the modulation of targets that regulate cholesterol metabolism, such as synthesis de novo, endocytosis, and oxidation, are contributing factors to cancer development. While mechanisms associated with sterol regulatory element-binding protein 2 (SREBP-2)/mevalonate, the low-density lipoprotein receptor (LDL-R) and liver X receptor (LXR) have been linked with tumor growth; metabolites derived from cholesterol-oxidation, such as oxysterols and epoxy-cholesterols, also have been described as tumor processes-inducers. From this notion, we perform an analysis of the role of lipoproteins, their association with intracellular cholesterol metabolism, and the impact of these conditions on breast cancer development, mechanisms that can be shared during atherogenesis promoted mainly by LDL. Pathways connecting plasma dyslipidemias in conjunction with the effect of cholesterol-derived metabolites on intracellular mechanisms and cellular plasticity phenomena could provide new approaches to elucidate the triggering factors of carcinogenesis, conditions that could be considered in the development of new therapeutic approaches.

Interferon-mediated Reprogramming of Intracellular Cholesterol Metabolism in Response to Secreted Bacterial Toxins

Abstract Macrophages undergo profound metabolic reprogramming in response to activation signals. However, the purpose and the mechanism of this reprogramming remains poorly understood. Cholesterol is an essential lipid molecule that modulates biochemical and biophysical properties of cellular membranes. Microbes have evolved strategies which specifically exploit the presence of membrane cholesterol to facilitate pathogenesis. Cholesterol-dependent cytolysin (CDC) are pore-forming toxins produced by gram-positive microorganisms that results in loss of membrane integrity, cellular dysfunction, and cell death. Herein, we delineate a unappreciated immune cell strategy that relies on rapid reprogramming of cholesterol homeostasis to avoid the deleterious effects CDCs. We show that interferon signals convey resistance to CDCs in myeloid cells by altering the availability of cholesterol in the plasma membrane (PM). Mechanistic studies reveal that resistance to CDCs occurs as a result of the movement of cholesterol from the PM to the endoplasmic reticulum (ER), and ultimately into an intracellular esterified pool. We also find that IFN-mediated inhibition of cholesterol synthesis is required to ensure maximal resistance to CDC challenge. Finally, we demonstrate that the IFN-mediated inhibition of cholesterol synthesis is dependent on production of the oxysterol, 25-hydroxycholesterol, and that the loss of CH25H renders mice more susceptible to CDC-mediated tissue damage. Together, these data provide evidence for remodeling of membrane lipid composition as a host defense strategy to bacterial toxins, and suggests that metabolic reprogramming of lipid architecture has significance beyond that of supporting immune function.

Disruption of Dhcr7 and Insig1/2 in cholesterol metabolism causes defects in bone formation and homeostasis through primary cilium formation

Human linkage studies suggest that craniofacial deformities result from either genetic mutations related to cholesterol metabolism or high-cholesterol maternal diets. However, little is known about the precise roles of intracellular cholesterol metabolism in the development of craniofacial bones, the majority of which are formed through intramembranous ossification. Here, we show that an altered cholesterol metabolic status results in abnormal osteogenesis through dysregulation of primary cilium formation during bone formation. We found that cholesterol metabolic aberrations, induced through disruption of either Dhcr7 (which encodes an enzyme involved in cholesterol synthesis) or Insig1 and Insig2 (which provide a negative feedback mechanism for cholesterol biosynthesis), result in osteoblast differentiation abnormalities. Notably, the primary cilia responsible for sensing extracellular cues were altered in number and length through dysregulated ciliary vesicle fusion in Dhcr7 and Insig1/2 mutant osteoblasts. As a consequence, WNT/β-catenin and hedgehog signaling activities were altered through dysregulated primary cilium formation. Strikingly, the normalization of defective cholesterol metabolism by simvastatin, a drug used in the treatment of cholesterol metabolic aberrations, rescued the abnormalities in both ciliogenesis and osteogenesis in vitro and in vivo. Thus, our results indicate that proper intracellular cholesterol status is crucial for primary cilium formation during skull formation and homeostasis.

Pharmacological and non pharmacological treatment of Alzheimer's disease

To date, only symptomatic treatments exist for Alzheimer’s disease. Pharmacological treatment aims to counterbalance the neurotransmitter disturbance. Three cholinesterase inhibitors (CIs) are currently available and have been approved for the treatment of mild to moderate AD. A further therapeutic option available is memantine, an N-methyl- D-aspartate receptor noncompetitive antagonist. Other symptomatic treatments can be used for the behavioral and psychiatric symptoms of the disease. Non-drug interventions include things like memory training, mental and social stimulation, and physical exercise programs. Some of these strategies could possibly improve people’s cognitive performance and increase their independence. Treatments capable of stopping or at least effectively modifying the course of AD, referred to as ‘disease-modifying’ drugs, are still under extensive research. To block the progression of the disease they have to interfere with the pathogenic steps responsible for the clinical symptoms, including the deposition of extracellular amyloid β plaques and intracellular neurofibrillary tangle formation, inflammation, oxidative damage, iron deregulation and cholesterol metabolism.

ABCA1 overexpression worsens colorectal cancer prognosis by facilitating tumour growth and caveolin‐1‐dependent invasiveness, and these effects can be ameliorated using the BET inhibitor apabetalone

At the time of diagnosis, 20% of patients with colorectal cancer present metastasis. Among individuals with primary lesions, 50% of them will develop distant tumours with time. Therefore, early diagnosis and prediction of aggressiveness is crucial for therapy design and disease prognosis. Tumoral cells must undergo significant changes in energy metabolism to meet increased structural and energetic demands for cell proliferation, and metabolic alterations are considered to be a hallmark of cancer. Here, we present the ATP‐binding cassette transporter (ABCA1), a regulator of cholesterol transport, as a new marker for invasion and colorectal cancer survival. ABCA1 is significantly overexpressed in patients at advanced stages of colorectal cancer, and its overexpression confers proliferative advantages together with caveolin‐1 dependent‐increased migratory and invasive capacities. Thus, intracellular cholesterol imbalances mediated by ABCA1 overexpression may contribute to primary tumour growth and dissemination to distant locations. Furthermore, we demonstrate here that increased levels of apolipoprotein A1 (APOA1), a protein involved in cholesterol efflux and high‐density lipoprotein constitution, in the extracellular compartment modulates expression of ABCA1 by regulating COX‐2, and compensate for ABCA1‐dependent excessive export of cholesterol. APOA1 emerges as a new therapeutic option to inhibit the promotion of colorectal cancer to metastasis by modulating intracellular cholesterol metabolism. Furthermore, we propose apabetalone, an orally available small molecule that is currently being evaluated in clinical trials for the treatment of atherosclerosis, as a new putative therapeutic option to prevent colorectal cancer progression by increasing APOA1 expression and regulating reverse transport of cholesterol.

Intracellular and Plasma Membrane Events in Cholesterol Transport and Homeostasis.

Cholesterol transport between intracellular compartments proceeds by both energy- and non-energy-dependent processes. Energy-dependent vesicular traffic partly contributes to cholesterol flux between endoplasmic reticulum, plasma membrane, and endocytic vesicles. Membrane contact sites and lipid transfer proteins are involved in nonvesicular lipid traffic. Only “active" cholesterol molecules outside of cholesterol-rich regions and partially exposed in water phase are able to fast transfer. The dissociation of partially exposed cholesterol molecules in water determines the rate of passive aqueous diffusion of cholesterol out of plasma membrane. ATP hydrolysis with concomitant conformational transition is required to cholesterol efflux by ABCA1 and ABCG1 transporters. Besides, scavenger receptor SR-B1 is involved also in cholesterol efflux by facilitated diffusion via hydrophobic tunnel within the molecule. Direct interaction of ABCA1 with apolipoprotein A-I (apoA-I) or apoA-I binding to high capacity binding sites in plasma membrane is important in cholesterol escape to free apoA-I. ABCG1-mediated efflux to fully lipidated apoA-I within high density lipoprotein particle proceeds more likely through the increase of “active” cholesterol level. Putative cholesterol-binding linear motifs within the structure of all three proteins ABCA1, ABCG1, and SR-B1 are suggested to contribute to the binding and transfer of cholesterol molecules from cytoplasmic to outer leaflets of lipid bilayer. Together, plasma membrane events and intracellular cholesterol metabolism and traffic determine the capacity of the cell for cholesterol efflux.

The Interplay Between Cholesterol Metabolism and Intrinsic Ageing.

The last few decades have witnessed remarkable progress in our understanding of ageing. From an evolutionary standpoint it is generally accepted that ageing is a non-adaptive process which is underscored by a decrease in the force of natural selection with time. From a mechanistic perspective ageing is characterized by a wide variety of cellular mechanisms, including processes such as cellular senescence, telomere attrition, oxidative damage, molecular chaperone activity, and the regulation of biochemical pathways by sirtuins. These biological findings have been accompanied by an unrelenting rise in both life expectancy and the number of older people globally. However, despite age being recognized demographically as a risk factor for healthspan, the processes associated with ageing are routinely overlooked in disease mechanisms. Thus, a central goal of biogerontology is to understand how diseases such as cardiovascular disease (CVD) are shaped by ageing. This challenge cannot be ignored because CVD is the main cause of morbidity in older people. A worthwhile way to examine how ageing intersects with CVD is to consider the effects ageing has on cholesterol metabolism, because dysregualted cholesterol metabolism is the key factor which underpins the pathology of CVD. The aim of this chapter is to outline a hypothesis which accounts for how ageing intersects with intracellular cholesterol metabolism. Moreover, we discuss the implications of this relationship for the onset of disease in the 'oldest old' (individuals ≥85years of age). We conclude the chapter by discussing the important role mathematical modelling has to play in improving our understanding of cholesterol metabolism and ageing.

Cholesterol-lowing effect of taurine in HepG2 cell

BackgroundA number of studies indicate that taurine promotes cholesterol conversion to bile acids by upregulating CYP7A1 gene expression. Few in vitro studies are concerned the concentration change of cholesterol and its product of bile acids, and the molecular mechanism of CYP7A1 induction by taurine.MethodsThe levels of intracellular total cholesterol (TC), free cholesterol (FC), cholesterol ester (EC), total bile acids (TBA) and medium TBA were determined after HepG2 cells were cultured for 24/48 h in DMEM supplemented with taurine at the final concentrations of 1/10/20 mM respectively. The protein expressions of CYP7A1, MEK1/2, c-Jun, p-c-Jun and HNF-4α were detected.ResultsTaurine significantly reduced cellular TC and FC in dose —and time-dependent ways, and obviously increased intracellular/medium TBA and CYP7A1 expressions. There was no change in c-Jun expression, but the protein expressions of MEK1/2 and p-c-Jun were increased at 24 h and inhibited at 48 h by 20 mM taurine while HNF4α was induced after both of the 24 h and 48 h treatment.ConclusionTaurine could enhance CYP7A1 expression by inducing HNF4α and inhibiting MEK1/2 and p-c-Jun expressions to promote intracellular cholesterol metabolism.