Player In Cholesterol Metabolism Research Articles

The Apo gene's genetic variants: hidden role in Asian vascular risk.

Vascular risk factors, including diabetes, hypertension, hyperlipidemia, and obesity, pose significant health threats with implications extending to neuropsychiatric disorders such as stroke and Alzheimer's disease. The Asian population, in particular, appears to be disproportionately affected due to unique genetic predispositions, as well as epigenetic factors such as dietary patterns and lifestyle habits. Existing management strategies often fall short of addressing these specific needs, leading to greater challenges in prevention and treatment. This review highlights a significant gap in our understanding of the impact of genetic screening in the early detection and tailored treatment of vascular risk factors among the Asian population. Apolipoprotein, a key player in cholesterol metabolism, is primarily associated with dyslipidemia, yet emerging evidence suggests its involvement in conditions such as diabetes, hypertension, and obesity. While genetic variants of vascular risk are ethnic-dependent, current evidence indicates that epigenetics also exhibits ethnic specificity. Understanding the interplay between Apolipoprotein and genetics, particularly within diverse ethnic backgrounds, has the potential to refine risk stratification and enhance precision in management. For Caucasian carrying the APOA5 rs662799 C variant, pharmacological interventions are recommended, as dietary interventions may not be sufficient. In contrast, for Asian populations with the same genetic variant, dietary modifications are initially advised. Should dyslipidemia persist, the consideration of pharmaceutical agents such as statins is recommended.

Elucidating APOE4‐dependent cholesterol dysregulation in endolysosomes related to Alzheimer’s disease biology

AbstractBackgroundAberrant cholesterol processing may be the missing link in the biology of AD, and in our understanding of AD etiology. APOE4 is a major genetic risk factor for AD, and a key player in cholesterol metabolism in the brain. Previous research from our group has shown that APOE4 is related to increased lysosomal cholesterol accumulation in human iPSC‐astrocytes, and altered endolysosomal morphology has been observed in the entorhinal cortex (EC) of aged APOE4 mice. However, it is unclear how endolysosomal cholesterol mistrafficking changes with age.MethodTherefore, we studied endolysosomal cholesterol accumulation in middle (15‐16month) and old age (25‐26month) old mice, enabling us to study these processes already in mid‐life. We used brain sections of humanized APOE mice, looking at different brain regions to study regional vulnerability and temporal progression. Cholesterol was labeled using the novel and highly specific D4H probe, enabling its quantification within the endolysosomal system using immunohistochemistry. Cholesterol and endolysosomal markers were quantified and colocalized using Cellprofiler.ResultOlder APOE4 mice showed an increase of total cholesterol in their brain, and specifically an increase of lysosomal cholesterol. Middle aged mice did not show a difference in total cholesterol, however, there was a specific decrease in early endosomal (EE) and late endosomal (LE) cholesterol only in the entorhinal cortex (EC) of female APOE3 mice, while lysosomal cholesterol was increased in this group (APOE4 and APOE2 showed similar levels). The EE and LE cholesterol differences were specific to neurons, but not the lysosomal cholesterol increase, indicating that non‐neuronal cells play a role. Another striking finding was the increase of neuronal EE cholesterol in the EC of middle aged APOE3 male vs female mice, whereas the reverse was seen in APOE4 brain tissue.ConclusionAltogether these results indicate that endolysosomal cholesterol is a dynamic process throughout aging, which may play and active role in AD biology. There is a noticeable shift from EE and EL cholesterol changes in midlife, to lysosomal cholesterol accumulation in older age, which are APOE‐genotype dependent. Notably, the EC specifically of female mice show the most variable endolysosomal cholesterol levels, and may be involved in increased vulnerability to pathology.

High-fat diet reveals the impact of Sar1b defects on lipid and lipoprotein profile and cholesterol metabolism

Biallelic pathogenic variants of the Sar1b gene cause chylomicron retention disease (CRD) whose central phenotype is the inability to secrete chylomicrons. Patients with CRD experience numerous clinical symptoms such as gastrointestinal, hepatic, neuromuscular, ophthalmic, and cardiological abnormalities. Recently, the production of mice expressing either a targeted deletion or mutation of Sar1b recapitulated biochemical and gastrointestinal defects associated with CRD. The present study was conducted to better understand little-known aspects of Sar1b mutations, including mouse embryonic development, lipid profile, and lipoprotein composition in response to high-fat diet, gut and liver cholesterol metabolism, sex-specific effects, and genotype-phenotype differences. Sar1b deletion and mutation produce a lethal phenotype in homozygous mice, which display intestinal lipid accumulation without any gross morphological abnormalities. On high-fat diet, mutant mice exhibit more marked abnormalities in body composition, adipose tissue and liver weight, plasma cholesterol, non-HDL cholesterol and polyunsaturated fatty acids than those on the regular Chow diet. Divergences were also noted in lipoprotein lipid composition, lipid ratios (serving as indices of particle size) and lipoprotein-apolipoprotein distribution. Sar1b defects significantly reduce gut cholesterol accumulation while altering key players in cholesterol metabolism. Noteworthy, variations were observed between males and females, and between Sar1b deletion and mutation phenotypes. Overall, mutant animal findings reveal the importance of Sar1b in several biochemical, metabolic and developmental processes.

Apolipoprotein E polymorphism influences orthotopic liver transplantation outcomes in patients with hepatitis C virus-induced liver cirrhosis.

BACKGROUNDHepatitis C virus (HCV) infection is responsible for a chronic liver inflammation, which may cause end-stage liver disease and hepatocellular carcinoma. Apolipoprotein E (protein: ApoE, gene: APOE), a key player in cholesterol metabolism, is mainly synthesized in the liver and APOE polymorphisms may influence HCV-induced liver damage. AIMTo determine whether APOE alleles affect outcomes in HCV-infected patients with liver cirrhosis following orthotopic liver transplantation (OLT). METHODSThis was a cohort study in which 179 patients, both genders and aged 34-70 years, were included before or after (up to 10 years follow-up) OLT. Liver injury severity was assessed using different criteria, including METAVIR and models for end-stage liver disease. APOE polymorphisms were analyzed by quantitative real-time polymerase chain reaction. RESULTSThe APOE3 allele was the most common (67.3%). In inflammation severity of biopsies from 89 OLT explants and 2 patients in pre-transplant, the degree of severe inflammation (A3F4, 0.0%) was significantly less frequent than in patients with minimal and moderate degree of inflammation (≤ A2F4, 16.2%) P = 0.048, in patients carrying the APOE4 allele when compared to non-APOE4. In addition, a significant difference was also found (≤ A2F4, 64.4% vs A3F4, 0.0%; P = 0.043) and (A1F4, 57.4% vs A3F4, 0.0%; P = 0.024) in APOE4 patients when compared to APOE3 carriers. The fibrosis degree of the liver graft in 8 of 91 patients and the lack of the E4 allele was associated with more moderate fibrosis (F2) (P = 0.006). CONCLUSIONOur results suggest that the E4 allele protects against progression of liver fibrosis and degree of inflammation in HCV-infected patients.

Abstract 19498: Scavenger Receptor BI (SR-BI) Deficiency Uncouples Obesity From Glucose Intolerance in Mice

Introduction: Scavenger receptor BI (SR-BI) is a multi-purpose player in cholesterol metabolism. Interestingly, several studies in humans have suggested that a significant relationship exists between the presence of common variants in the SR-BI gene and a higher body mass index. We therefore evaluated the contribution of SR-BI to high fat diet-induced obesity in mice. Methods and Results: Male SR-BI knockout (SR-BI KO; N=10) and wild-type (WT; N=9) mice were fed a diet containing 45% energy as fat for 12 weeks. SR-BI KO mice exhibited a worsened metabolic plasma profile as compared to WT controls with higher fasting levels of free cholesterol (+111%; P<0.001), cholesterol esters (+84%; P<0.001), triglycerides (+40%; P<0.01), and glucose (+20%; P<0.01). Daily food intake was similar in the two types of mice; 4.5±0.3 g for SR-BI KO vs 4.1±0.3 g for WT. Importantly, the relative increase in body weight over time was significantly greater in SR-BI KO mice (+51%) as compared to WT controls (+33%; two-way ANOVA P<0.001 for genotype). The exacerbated increase in body weight could be attributed to a higher white adipose tissue mass (correlation coefficient R=0.87; P<0.001). High fat diet-fed WT mice were glucose intolerant, but remained resistant to atherosclerosis. In contrast, atherosclerotic lesions could be readily detected in the aortic root of SR-BI KO mice (6.9±1.5 x 10 3 μm 2 ; P<0.001), while their glucose tolerance was remarkably higher compared to that of controls (oral glucose tolerance test AUC 484±68 mM.min for SR-BI KO vs 875±130 mM.min for WT; P<0.05). SR-BI deficiency thus uncouples obesity from glucose intolerance in mice. Conclusions: Our studies for the first time show that a proper SR-BI function inhibits the development of obesity in mice. Furthermore, these data imply that SR-BI may serve as therapeutic target to overcome the glucose intolerance normally associated with the presence of (morbid) obesity.

PCSK9 inhibition: the way forward in the treatment of dyslipidemia.

Barely a decade after the discovery of the gene encoding proprotein convertase subtilisin/kexin type 9 (PCSK9) and its recognition as a key player in cholesterol metabolism, PCSK9 inhibition is now considered an exciting approach in the reduction of residual risk of cardiovascular disease. The progress from PCSK9 discovery to the development of targeted treatment has been unprecedented in terms of scale and speed. The first suggestion of a link between PCSK9 and hypercholesterolemia was published in 2003; a decade later, two meta-analyses of clinical trials comparing anti-PCSK9 treatment to placebo or ezetimibe, including >10,000 hypercholesterolemic individuals, were published. Currently, three PCSK9 inhibitors are being evaluated in clinical outcome trials and the results will determine the future of these lipid-lowering therapies by establishing their clinical efficacy in terms of cardiovascular event reduction, safety, and the consequences of prolonged exposure to very low levels of LDL-cholesterol. Irrespective of their outcomes, the exceptionally rapid development of these drugs exemplifies how novel technologies, genetic validation, and rapid clinical progression provide the tools to expedite the development of new drugs.

Abstract LB-3: Apolipoprotein (E) is a determinant of colon carcinogenesis potentially by regulating inflammation and β-catenin independently of its role in lipid metabolism

Abstract Colorectal cancer is a leading cause of cancer-related mortality. Apolipoprotein E (ApoE) is a major player in cholesterol metabolism and has been suggested, through association studies, to play a role in colon homoeostasis and cancer. Genetic studies suggested that polymorphisms in the ApoE alleles constitute a risk factor for the development of colon cancer. Collectively, these studies explored the role of ApoE in colon cancer by narrowly focusing on its established function in lipid metabolism. In the current study, we utilized a genetic mouse model (ApcMin mouse) of colon cancer to test the hypothesis that ApoE is a determinant in the disease progression. We show that ApoE gene heterozygosity, which reduces the protein (∼50%) and minimally affects the lipid profile, significantly increased tumor burden in ApcMin mice both in the small intestine and the colon. Surprisingly, ApoE gene knockout, which completely eliminates the protein and drastically elevates the lipid profile, did not aggravate the tumor burden in ApcMin mice compared to that caused by gene heterozygosity, suggesting a novel and cholesterol-metabolism-independent function for ApoE in colon homeostasis. In vitro studies with primary colon epithelial cells, isolated using a novel technique developed by our laboratory, show that ApoE-deficiency achieved by ApoE heterozygosity, knockout, or knockdown increased the level of active β-catenin in the absence of any stimulation. It appears that such increase in β-catenin may be at an mRNA level. ApoE deficiency was also associated with an increase in inflammatory factors including VCAM-1, MCP-1, and COX-2 in TNF-treated colon epithelial cells. Altogether, our preliminary results suggest a major role of ApoE in colon homeostasis and that deficiency in ApoE levels may constitute a risk factor for colon cancer progression. Citation Format: Ali I. Elbahrawy, Abdelmetalab Tarhuni, Amarjit S. Naura, Youssef Errami, Mohamed Alwan, Samar Hammad, Jimena Trillo-Tinoco, Ramadan Hemeida, Hassan Brim, Hassan Ashktorab, Luis Del Valle, Hamid A. Boulares. Apolipoprotein (E) is a determinant of colon carcinogenesis potentially by regulating inflammation and β-catenin independently of its role in lipid metabolism. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-3. doi:10.1158/1538-7445.AM2014-LB-3

The StarD4 subfamily of steroidogenic acute regulatory-related lipid transfer (START) domain proteins: New players in cholesterol metabolism

Cholesterol levels in the body are maintained through the coordinated regulation of its uptake, synthesis, distribution, storage and efflux. However, the way cholesterol is sorted within cells remains poorly defined. The discovery of the newly described StarD4 subfamily, part of the steroidogenic acute regulatory lipid transfer (START) domain family of proteins, affords an opportunity for the study of intracellular cholesterol movement, metabolism and its disorders. The three members of this intracellular subfamily of proteins (StarD4, StarD5 and StarD6) have a similar lipid binding pocket specific for sterols (cholesterol in particular), but differing regulation and localization. The ability to bind and transport cholesterol through a non-vesicular mean suggests that they play a previously unappreciated role in cholesterol homeostasis.

Ubiquitin ligases in cholesterol metabolism.

To maintain cholesterol homeostasis, the processes of cholesterol metabolism are regulated at multiple levels including transcription, translation, and enzymatic activity. Recently, the regulation of protein stability of some key players in cholesterol metabolism has been characterized. More and more ubiquitin ligases have been identified including gp78, Hrd1, TRC8, TEB4, Fbw7, and inducible degrader of low density lipoprotein receptor. Their working mechanisms and physiological functions are becoming revealed. Here, we summarize the structure, substrates and function of these ubiquitin ligases. Their potential application in drug discovery is also discussed.

Leishmania Dices Away Cholesterol for Survival

Host lipid alterations are centrally involved in Leishmania donovani infection, and infected patients exhibit hypocholesterolemia. In this issue of Cell Host & Microbe, Ghosh etal. (2013) show that the metalloprotease GP63 released by L.donovani in the liver cleaves DICER1, inhibiting miR-122 maturation, which regulates cholesterol metabolism. These events decrease serum cholesterol and promote parasite growth.

The Conserved Rieske Oxygenase DAF-36/Neverland Is a Novel Cholesterol-metabolizing Enzyme

Steroid hormones play essential roles in a wide variety of biological processes in multicellular organisms. The principal steroid hormones in nematodes and arthropods are dafachronic acids and ecdysteroids, respectively, both of which are synthesized from cholesterol as an indispensable precursor. The first critical catalytic step in the biosynthesis of these ecdysozoan steroids is the conversion of cholesterol to 7-dehydrocholesterol. However, the enzymes responsible for cholesterol 7,8-dehydrogenation remain unclear at the molecular level. Here we report that the Rieske oxygenase DAF-36/Neverland (Nvd) is a cholesterol 7,8-dehydrogenase. The daf-36/nvd genes are evolutionarily conserved, not only in nematodes and insects but also in deuterostome species that do not produce dafachronic acids or ecdysteroids, including the sea urchin Hemicentrotus pulcherrimus, the sea squirt Ciona intestinalis, the fish Danio rerio, and the frog Xenopus laevis. An in vitro enzymatic assay system reveals that all DAF-36/Nvd proteins cloned so far have the ability to convert cholesterol to 7-dehydrocholesterol. Moreover, the lethality of loss of nvd function in the fruit fly Drosophila melanogaster is rescued by the expression of daf-36/nvd genes from the nematode Caenorhabditis elegans, the insect Bombyx mori, or the vertebrates D. rerio and X. laevis. These data suggest that daf-36/nvd genes are functionally orthologous across the bilaterian phylogeny. We propose that the daf-36/nvd family of proteins is a novel conserved player in cholesterol metabolism across the animal phyla.