Regulation Of Plasma Cholesterol Levels Research Articles

Effects of Walnut Septum on The Enzyme Pathways Associated with Plasma Cholesterol Level

Objective: Cholesterol is crucial compound that plays pivotal role in cellular function in living organisms. Its excess or deficiency in plasma can lead to destruction and disintegration of cell membrane structure. Maintaining balanced intake of cholesterol in diet and seeking medical treatment, if necessary, can help prevent these negative effects. Furthermore, people often resort to natural and herbal remedies, such as walnut septum. Due to dearth of scientific data regarding effects of walnut septum on cholesterol metabolism, this research was undertaken to explore its potential effects. Method: Analysis was begun by extracting septum using various solvents. Resulting extracts were then analyzed using GC-MS, and compounds were identified by using an integrated library database. To detect effects of extracts on cholesterol esterase and HMG-CoA reductase, a colorimetric method was employed. Result: Monophenol, 2,4-Di-tert-butylphenol, 2,6-Di-tert-butylphenol, ethyl linoleate, and butyl linoleate were some of compounds detected by GC-MS scanning. The highest inhibitions were observed in the enzymatic analysis, with a rate of 3.2% (acetone) in the HMG-CoA reductase analysis and 13.6% (water) in the cholesterol esterase analysis. Conclusion: Although the walnut septum extract contains various chemical compounds, our in vitro analysis data suggest that there is no inhibitory effect at therapeutic level on enzyme pathways that regulate plasma cholesterol levels, namely HMG-CoA reductase and cholesterol esterase. We believe that further research is necessary to comprehensively evaluate its effects on other pathways.

Mechanism of the Regulation of Plasma Cholesterol Levels by PI(4,5)P2.

Elevated low-density lipoprotein (LDL) cholesterol (LDLc) is one of the most well-established risk factors for cardiovascular disease, while high levels of high-density lipoprotein (HDL) cholesterol (HDLc) have been associated with protection from cardiovascular disease. Cardiovascular disease remains one of the leading causes of death worldwide; thus it is important to understand mechanisms that impact LDLc and HDLc metabolism. In this chapter, we will discuss molecular processes by which phosphatidylinositol-(4,5)-bisphosphate, PI(4,5)P2, is thought to modulate LDLc or HDLc. Section 1 will provide an overview of cholesterol in the circulation, discussing processes that modulate the various forms of lipoproteins (LDL and HDL) carrying cholesterol. Section 2 will describe how a PI(4,5)P2 phosphatase, transmembrane protein 55B (TMEM55B), impacts circulating LDLc levels through its ability to regulate lysosomal decay of the low-density lipoprotein receptor (LDLR), the primary receptor for hepatic LDL uptake. Section 3 will discuss how PI(4,5)P2 interacts with apolipoprotein A-I (apoA1), the key apolipoprotein on HDL. In addition to direct mechanisms of PI(4,5)P2 action on circulating cholesterol, Sect. 4 will review how PI(4,5)P2 may indirectly impact LDLc and HDLc by affecting insulin action. Last, as cholesterol is controlled through intricate negative feedback loops, Sect. 5 will describe how PI(4,5)P2 is regulated by cholesterol.

Identification of Target Genes for Retinoid-related Orphan Receptors Involved in the Suppression of Atherosclerosis

Retinoid-related orphan receptor alpha (RORα) participates in regulating several physiological processes, including metabolism and circadian rhythms. RORα is an important regulator of plasma cholesterol levels and is involved in lipid homeostasis. Its activation increases high-density lipoprotein (HDL) levels and metabolism of oxysterols. RORα-deficient mice develop atherosclerosis owing to decreased plasma HDL levels, increased expression of inflammatory cytokines, and ischemia/reperfusion-induced damage. The transcriptional activity of RORα is controlled by cholesterol and its derivatives, endogenous ligands that form transcription initiation complexes. Conversely, when intracellular cholesterol is reduced by lipid-lowering drugs such as statins, which inhibit cholesterol synthesis, the transcriptional activity of RORα is attenuated. Therefore, studies have focused on identifying target genes regulated by RORα involved in alleviating atherosclerosis to develop new therapies. Characterization of ligands, transcription-mediating factors, and transcription initiation complexes involved in the transcriptional regulation of RORα will facilitate the development of synthetic ligands and their potential applications in diseases such as atherosclerosis, dyslipidemia, and diabetes. In this review, we discuss the current literature on the structure and function of RORα, the target genes regulated by RORα, and the potential of RORα as a therapeutic target for atherosclerosis.

From fatty streaks to culprit lesions, the impact of PCSK9 on human atherosclerotic lesions through smooth muscle cells functions

Background and Aims : PCSK9 is the third gene involved in familial hypercholesterolemia, a major cause of atherosclerosis. Its role in regulating plasma cholesterol levels has been widely reported, and anti-PCSK9 drugs have been developed. Nevertheless, direct interactions between PCSK9 and atherosclerotic pathology are not fully elucidated. We aim at demonstrating that PCSK9 promotes atherosclerosis through vascular smooth muscle cells (VSMC) involved in foam cells formation, atherosclerosis initiation, and progression.

Inhibition of PCSK9 affects serum lipoprotein functions in patients with familial hypercholesterolemia

Background and Aims : PCSK9, beyond regulating plasma cholesterol levels, exerts several pleiotropic effects modulating lipid metabolism in extrahepatic cells, including macrophages. Macrophage cholesterol homeostasis strictly depends on serum lipoprotein functions, including the HDL capacity to promote cell cholesterol efflux (cholesterol efflux capacity, CEC) and the serum capacity to promote cell cholesterol accumulation (cholesterol loading capacity, CLC). The aim of the present study was to evaluate potential changes in HDL-CEC and serum CLC after six-month of treatment with PCSK9 inhibitors in Familial Hypercholesterolemia (FH) subjects.

Membrane type 1 matrix metalloproteinase promotes LDL receptor shedding and accelerates the development of atherosclerosis

Plasma low-density lipoprotein (LDL) is primarily cleared by LDL receptor (LDLR). LDLR can be proteolytically cleaved to release its soluble ectodomain (sLDLR) into extracellular milieu. However, the proteinase responsible for LDLR cleavage is unknown. Here we report that membrane type 1-matrix metalloproteinase (MT1-MMP) co-immunoprecipitates and co-localizes with LDLR and promotes LDLR cleavage. Plasma sLDLR and cholesterol levels are reduced while hepatic LDLR is increased in mice lacking hepatic MT1-MMP. Opposite effects are observed when MT1-MMP is overexpressed. MT1-MMP overexpression significantly increases atherosclerotic lesions, while MT1-MMP knockdown significantly reduces cholesteryl ester accumulation in the aortas of apolipoprotein E (apoE) knockout mice. Furthermore, sLDLR is associated with apoB and apoE-containing lipoproteins in mouse and human plasma. Plasma levels of sLDLR are significantly increased in subjects with high plasma LDL cholesterol levels. Thus, we demonstrate that MT1-MMP promotes ectodomain shedding of hepatic LDLR, thereby regulating plasma cholesterol levels and the development of atherosclerosis.

MicroRNA 27a Is a Key Modulator of Cholesterol Biosynthesis.

Hypercholesterolemia is a strong predictor of cardiovascular diseases. The 3-hydroxy-3-methylglutaryl coenzyme A reductase gene (Hmgcr) coding for the rate-limiting enzyme in the cholesterol biosynthesis pathway is a crucial regulator of plasma cholesterol levels. However, the posttranscriptional regulation of Hmgcr remains poorly understood. The main objective of this study was to explore the role of microRNAs (miRNAs) in the regulation of Hmgcr expression. Systematic in silico predictions and experimental analyses reveal that miRNA 27a (miR-27a) specifically interacts with the Hmgcr 3' untranslated region in murine and human hepatocytes. Moreover, our data show that Hmgcr expression is inversely correlated with miR-27a levels in various cultured cell lines and in human and rodent tissues. Actinomycin D chase assays and relevant experiments demonstrate that miR-27a regulates Hmgcr by translational attenuation followed by mRNA degradation. Early growth response 1 (Egr1) regulates miR-27a expression under basal and cholesterol-modulated conditions. miR-27a augmentation via tail vein injection of miR-27a mimic in high-cholesterol-diet-fed Apoe-/- mice shows downregulation of hepatic Hmgcr and plasma cholesterol levels. Pathway and gene expression analyses show that miR-27a also targets several other genes (apart from Hmgcr) in the cholesterol biosynthesis pathway. Taken together, miR-27a emerges as a key regulator of cholesterol biosynthesis and has therapeutic potential for the clinical management of hypercholesterolemia.

Phosphatidylinositol-(4,5)-Bisphosphate Regulates Plasma Cholesterol Through LDL (Low-Density Lipoprotein) Receptor Lysosomal Degradation.

TMEM55B (transmembrane protein 55B) is a phosphatidylinositol-(4,5)-bisphosphate (PI[4,5]P2) phosphatase that regulates cellular cholesterol, modulates LDLR (low-density lipoprotein receptor) decay, and lysosome function. We tested the effects of Tmem55b knockdown on plasma lipids in mice and assessed the roles of LDLR lysosomal degradation and change in (PI[4,5]P2) in mediating these effects. Approach and Results: Western diet-fed C57BL/6J mice were treated with antisense oligonucleotides against Tmem55b or a nontargeting control for 3 to 4 weeks. Hepatic Tmem55b transcript and protein levels were reduced by ≈70%, and plasma non-HDL (high-density lipoprotein) cholesterol was increased ≈1.8-fold (P<0.0001). Immunoblot analysis of fast protein liquid chromatography (FPLC) fractions revealed enrichment of ApoE-containing particles in the LDL size range. In contrast, Tmem55b knockdown had no effect on plasma cholesterol in Ldlr-/- mice. In primary hepatocytes and liver tissues from Tmem55b knockdown mice, there was decreased LDLR protein. In the hepatocytes, there was increased lysosome staining and increased LDLR-lysosome colocalization. Impairment of lysosome function (incubation with NH4Cl or knockdown of the lysosomal proteins LAMP1 or RAB7) abolished the effect of TMEM55B knockdown on LDLR in HepG2 (human hepatoma) cells. Colocalization of the recycling endosome marker RAB11 (Ras-related protein 11) with LDLR in HepG2 cells was reduced by 50% upon TMEM55B knockdown. Finally, knockdown increased hepatic PI(4,5)P2 levels in vivo and in HepG2 cells, while TMEM55B overexpression in vitro decreased PI(4,5)P2. TMEM55B knockdown decreased, whereas overexpression increased, LDL uptake in HepG2 cells. Notably, the TMEM55B overexpression effect was reversed by incubation with PI(4,5)P2. Conclusions: These findings indicate a role for TMEM55B in regulating plasma cholesterol levels by affecting PI(4,5)P2-mediated LDLR lysosomal degradation.

PCSK9 Inhibition and Atherosclerosis: Current Therapeutic Option and Prospection.

Low-density lipoprotein cholesterol (LDL-C) is a pivotal factor in atherosclerotic cardiovascular disease (ASCVD), the leading cause of worldwide mortality. The limitations of statin therapy require alternative treatment strategies to achieve target LDL-C level. Proprotein convertase subtilisin/kexin type 9 (PCSK9) plays an important role in LDLR recycling, consequently regulating plasma cholesterol levels. Monoclonal antibodies targeting PCSK9 increased expression of LDLRs at the cell surface and therefore decreased circulating LDL-C. PCSK9 inhibitors have shown great efficacy in reducing plasma LDL-C levels, which needs to inject once or twice monthly. Though SPIRE sponsors concern the immunogenicity and terminate trials early, FOURIER and ODYSSER OUTCOME trials improved the efficacy of PCSK9 inhibitors in LDL-C reduction. Inclisiran actually is a small interfering RNA (siRNA) developed to inhibit PCSK9 messenger RNA, leading to reduced concentrations of the PCSK9 protein and thereby lower concentrations of LDL-C. Inclisiran is a latest alternative treatment to cholesterol-lowering therapeutics. Twice injections of inclisiran durably reduced LDL-C levels over 1year. siRNA therapeutics provided a simple, novel, and less frequent approach to LDL-C reduction in phase I and II trials, which may be used either as in combination with statin therapeutics or a stand-alone therapy in the future.

Proprotein Convertase Subtilisin/Kexin-Type 9 and Lipid Metabolism.

Plasma levels of cholesterol, especially low-density lipoprotein cholesterol (LDL-C), are positively correlated with the risk of cardiovascular disease. Buildup of LDL in the intima promotes the formation of foam cells and consequently initiates atherosclerosis, one of the main underlying causes of cardiovascular disease. Hepatic LDL receptor (LDLR) is mainly responsible for the clearance of plasma LDL. Mutations in LDLR cause familiar hypercholesterolemia and increase the risk of premature coronary heart disease. Proprotein convertase subtilisin/kexin-type 9 (PCSK9) promotes LDLR degradation and thereby plays a critical role in the regulation of plasma cholesterol metabolism. PCSK9 can bind to LDLR and reroute the receptor to lysosomes for degradation, increasing both circulating LDL-C levels and the risk of cardiovascular disease. PCSK9 is mainly regulated by sterol response element binding protein 2 (SREBP2) at the transcriptional level. Furthermore, many proteins have been identified as interacting with PCSK9, regulating plasma cholesterol levels. Pharmacotherapeutic inhibition of PCSK9 dramatically reduces plasma levels of LDL cholesterol and significantly reduces cardiovascular events. In this article, we summarize the latest advances in PCSK9, mainly focusing on the structure, function, and regulation of the protein, the underlying molecular mechanisms, and its pharmacotherapeutic applications.

Deletion of the Mir-106b~\u200925 MicroRNA cluster attenuates atherosclerosis in Apolipoprotein E knockout mice

BackgroundMicroRNAs are short non-coding RNAs that regulate gene expression. The aim of this study was to gain an understanding of the possible role of the miR-106b~ 25 microRNA cluster in regulating atherosclerosis in mice.MethodsMiR-106b~ 25 knockout mice were outcrossed into Apolipoprotein E (ApoE) knockout background to generate double knockout mice. At 36 weeks of age, lesion size was evaluated in the aortic sinus by oil-red-O staining.ResultsLesion size was 2-fold smaller in double KO mice in comparison to ApoE KO mice. In addition, collagen staining showed a trend towards a stable plaque phenotype in the double KO mice. Lipid profiling of plasma samples of double KO and ApoE KO mice using FPLC revealed over 2-fold decrease in Very low density lipoprotein (VLDL) cholesterol content and a 50% decrease in low density lipoprotein (LDL) cholesterol content in double KO mice. By using target prediction software, we have identified several possible targets for the miR-106b~ 25 cluster including the VLDL and LDL receptors. We found that upon feeding miR-106b~ 25 KO mice with high fat diet, the expression of LDL and VLDL receptors was higher than in the wild-type mice, suggesting the miR-106b~ 25 cluster regulates atherosclerosis by influencing clearance of VLDL and LDL from the plasma.ConclusionsWe identified the miR-106b~ 25 cluster as a novel regulator of atherosclerosis in ApoE KO mice, presumably by regulating plasma cholesterol levels.

Small Interfering RNA Therapeutic Inclisiran: A New Approach to Targeting PCSK9.

Hypercholesterolemia is a leading cause of cardiovascular disease and mortality in men and women throughout the USA and abroad. The development of statins (HMG-CoA reductase inhibitors) to lower plasma atherogenic cholesterol levels and improve cardiovascular outcomes represents one of the greatest contributions to clinical science in the twentieth century, although residual risk remains even among statin-treated patients. Our understanding of lipid metabolism took a giant leap forward in 2003 with the discovery of proprotein convertase subtilsin/kexin type9 (PCSK9), a low abundance circulating protein with an outsized effect on the regulation of plasma cholesterol levels. Evolocumab and alirocumab represent the first two US Food and Drug Administration-approved fully human monoclonal antibodies that target PCSK9, which not only lower low-density lipoprotein (LDL) cholesterol to unprecedented levels, but also further improve important cardiovascular outcomes. Small interfering RNA (siRNA) molecules now represent the next generation of drugs designed to antagonize PCSK9. Inclisiran is a siRNA specific for PCSK9 that prevents translation of PCSK9 messenger RNA, leading to decreased concentrations of the protein and lower concentrations of LDL cholesterol. The ORION clinical development program includes several completed and ongoing clinical trials designed to evaluate the safety and efficacy of inclisiran and test its ability to improve hard cardiovascular outcomes. This review discusses the mechanisms of action of inclisiran, examines the current evidence, and provides a comparison of similarities and differences relative to the PCSK9 inhibitors.

Bone morphogenetic protein 1 cleaves the linker region between ligand-binding repeats 4 and 5 of the LDL receptor and makes the LDL receptor non-functional.

The cell-surface low-density lipoprotein receptor (LDLR) internalizes low-density lipoprotein (LDL) by receptor-mediated endocytosis and plays a key role in the regulation of plasma cholesterol levels. The ligand-binding domain of the LDLR contains seven ligand-binding repeats of approximately 40 residues each. Between ligand-binding repeats 4 and 5, there is a 10-residue linker region that is subject to enzymatic cleavage. The cleaved LDLR is unable to bind LDL. In this study, we have screened a series of enzyme inhibitors in order to identify the enzyme that cleaves the linker region. These studies have identified bone morphogenetic protein 1 (BMP1) as being the cleavage enzyme. This conclusion is based upon the use of the specific BMP1 inhibitor UK 383367, silencing of the BMP1 gene by the use of siRNA or CRISPR/Cas9 technology and overexpression of wild-type BMP1 or the loss-of-function mutant E214A-BMP1. We have also shown that the propeptide of BMP1 has to be cleaved at RSRR120↓ by furin-like proprotein convertases for BMP1 to have an activity towards the LDLR. Targeting BMP1 could represent a novel strategy to increase the number of functioning LDLRs in order to lower plasma LDL cholesterol levels. However, a concern by using BMP1 inhibitors as cholesterol-lowering drugs could be the risk of side effects based on the important role of BMP1 in collagen assembly.

The COMMD Family Regulates Plasma LDL Levels and Attenuates Atherosclerosis Through Stabilizing the CCC Complex in Endosomal LDLR Trafficking.

COMMD (copper metabolism MURR1 domain)-containing proteins are a part of the CCC (COMMD-CCDC22 [coiled-coil domain containing 22]-CCDC93 [coiled-coil domain containing 93]) complex facilitating endosomal trafficking of cell surface receptors. Hepatic COMMD1 inactivation decreases CCDC22 and CCDC93 protein levels, impairs the recycling of the LDLR (low-density lipoprotein receptor), and increases plasma low-density lipoprotein cholesterol levels in mice. However, whether any of the other COMMD members function similarly as COMMD1 and whether perturbation in the CCC complex promotes atherogenesis remain unclear. The main aim of this study is to unravel the contribution of evolutionarily conserved COMMD proteins to plasma lipoprotein levels and atherogenesis. Using liver-specific Commd1, Commd6, or Commd9 knockout mice, we investigated the relation between the COMMD proteins in the regulation of plasma cholesterol levels. Combining biochemical and quantitative targeted proteomic approaches, we found that hepatic COMMD1, COMMD6, or COMMD9 deficiency resulted in massive reduction in the protein levels of all 10 COMMDs. This decrease in COMMD protein levels coincided with destabilizing of the core (CCDC22, CCDC93, and chromosome 16 open reading frame 62 [C16orf62]) of the CCC complex, reduced cell surface levels of LDLR and LRP1 (LDLR-related protein 1), followed by increased plasma low-density lipoprotein cholesterol levels. To assess the direct contribution of the CCC core in the regulation of plasma cholesterol levels, Ccdc22 was deleted in mouse livers via CRISPR/Cas9-mediated somatic gene editing. CCDC22 deficiency also destabilized the complete CCC complex and resulted in elevated plasma low-density lipoprotein cholesterol levels. Finally, we found that hepatic disruption of the CCC complex exacerbates dyslipidemia and atherosclerosis in ApoE3*Leiden mice. Collectively, these findings demonstrate a strong interrelationship between COMMD proteins and the core of the CCC complex in endosomal LDLR trafficking. Hepatic disruption of either of these CCC components causes hypercholesterolemia and exacerbates atherosclerosis. Our results indicate that not only COMMD1 but all other COMMDs and CCC components may be potential targets for modulating plasma lipid levels in humans.

Differential effects of Calca-derived peptides in male mice with diet-induced obesity.

Key metabolic hormones, such as insulin, leptin, and adiponectin, have been studied extensively in obesity, however the pathophysiologic relevance of the calcitonin family of peptides remains unclear. This family includes calcitonin (CT), its precursor procalcitonin (PCT), and alpha calcitonin-gene related peptide (αCGRP), which are all encoded by the gene Calca. Here, we studied the role of Calca-derived peptides in diet-induced obesity (DIO) by challenging Calcr−/− (encoding the calcitonin receptor, CTR), Calca−/−, and αCGRP−/− mice and their respective littermates with high-fat diet (HFD) feeding for 16 weeks. HFD-induced pathologies were assessed by glucose tolerance, plasma cytokine and lipid markers, expression studies and histology. We found that DIO in mice lacking the CTR resulted in impaired glucose tolerance, features of enhanced nonalcoholic steatohepatitis (NASH) and adipose tissue inflammation compared to wildtype littermates. Furthermore, CTR-deficient mice were characterized by dyslipidemia and elevated HDL levels. In contrast, mice lacking Calca were protected from DIO, NASH and adipose tissue inflammation, and displayed improved glucose tolerance. Mice exclusively lacking αCGRP displayed a significantly less improved DIO phenotype compared to Calca-deficient mice. In summary, we demonstrate that the CT/CTR axis is involved in regulating plasma cholesterol levels while Calca, presumably through PCT, seems to have a detrimental effect in the context of metabolic disease. Our study provides the first comparative analyses of the roles of Calca-derived peptides and the CTR in metabolic disease.

Brain Control of Plasma Cholesterol Involves Polysialic Acid Molecules in the Hypothalamus.

The polysialic acid (PSA) is a large glycan that is added to cell-surface proteins during their post-translational maturation. In the brain, PSA modulates distances between cells and controls the plasticity of the nervous system. In the hypothalamus, PSA is involved in many aspects of energy balance including food intake, osmoregulation, circadian rhythm, and sleep. In this work, we investigated the role of hypothalamic PSA in the regulation of plasma cholesterol levels and distribution. We report that HFD consumption in mice rapidly increased plasma cholesterol, including VLDL, LDL, and HDL-cholesterol. Although plasma VLDL-cholesterol was normalized within the first week, LDL and HDL were still elevated after 2 weeks upon HFD. Importantly, we found that hypothalamic PSA removal aggravated LDL elevation and reduced HDL levels upon HFD. These results indicate that hypothalamic PSA controls plasma lipoprotein profile by circumventing the rise of LDL-to-HDL cholesterol ratio in plasma during overfeeding. Although mechanisms by which hypothalamic PSA controls plasma cholesterol homeostasis remains to be elucidated, these findings also suggest that low level of hypothalamic PSA might be a risk factor for dyslipidemia and cardiovascular diseases.

Regulation of lipid metabolism by obeticholic acid in hyperlipidemic hamsters

The farnesoid X receptor (FXR) plays critical roles in plasma cholesterol metabolism, in particular HDL-cholesterol (HDL-C) homeostasis. Obeticholic acid (OCA) is a FXR agonist being developed for treating various chronic liver diseases. Previous studies reported inconsistent effects of OCA on regulating plasma cholesterol levels in different animal models and in different patient populations. The mechanisms underlying its divergent effects have not yet been thoroughly investigated. The scavenger receptor class B type I (SR-BI) is a FXR-modulated gene and the major receptor for HDL-C. We investigated the effects of OCA on hepatic SR-BI expression and correlated such effects with plasma HDL-C levels and hepatic cholesterol efflux in hyperlipidemic hamsters. We demonstrated that OCA induced a time-dependent reduction in serum HDL-C levels after 14 days of treatment, which was accompanied by a significant reduction of liver cholesterol content and increases in fecal cholesterol in OCA-treated hamsters. Importantly, hepatic SR-BI mRNA and protein levels in hamsters were increased to 1.9- and 1.8-fold of control by OCA treatment. Further investigations in normolipidemic hamsters did not reveal OCA-induced changes in serum HDL-C levels or hepatic SR-BI expression. We conclude that OCA reduces plasma HDL-C levels and promotes transhepatic cholesterol efflux in hyperlipidemic hamsters via a mechanism involving upregulation of hepatic SR-BI.

Calorically restricted diets decrease PCSK9 in overweight adolescents

Background and aimsNutritional therapy is the first line approach to treatment of hyperlipidemia in childhood. Proprotein convertase subtilisin kexin type 9 (PCSK9) is a key regulator of plasma cholesterol levels and a target of novel lipid-lowering pharmacotherapies. We examined the effects of an intensive nutritional intervention on PCSK9 levels in overweight adolescents with cardiovascular disease (CVD) risk factors. Methods and resultsTwenty seven obese and overweight adolescents with CVD risk factors were assigned to either a low fat or low glycemic load diet. During an 8-week “Intensive Phase,” assigned meals were delivered to the home, and all participants received weekly in-person home nutrition counseling and phone calls. The subjects then underwent a 4-month “Maintenance Phase” without food provision and with no in-person contact. Anthropometric measurements, laboratory data, and serum PCSK9 protein levels were measured at baseline, 8 weeks, and 6 months. PCSK9 decreased by 16.5% at 8 weeks (201.2 ± 56.3 vs 165.6 ± 58.4 ng/mL; p < 0.001); PCSK9 levels returned to baseline levels at 6 months, after the Maintenance Phase. Change in PCSK9 was associated with change in fasting insulin, HOMA-IR, and AUC insulin, independent of weight loss. ConclusionsPCSK9 decreased in youth participating in an intensive dietary intervention. Change in HOMA-IR was associated with change in PCSK9, independent of weight loss, suggesting an important relationship with insulin sensitivity.ClinicalTrials.gov Identifier: NCT01080339.

The Role of Proprotein Convertase Subtilisin/Kexin Type 9 in Nephrotic Syndrome-Associated Hypercholesterolemia.

In nephrotic syndrome, damage to the podocytes of the kidney produces severe hypercholesterolemia for which novel treatments are urgently needed. PCSK9 (proprotein convertase subtilisin/kexin type 9) has emerged as an important regulator of plasma cholesterol levels and therapeutic target. Here, we tested the role of PCSK9 in mediating the hypercholesterolemia of nephrotic syndrome. PCSK9 and plasma lipids were studied in nephrotic syndrome patients before and after remission of disease, mice with genetic ablation of the podocyte (Podocyte Apoptosis Through Targeted Activation of Caspase-8, Pod-ATTAC mice) and mice treated with nephrotoxic serum (NTS), which triggers immune-mediated podocyte damage. In addition, mice with hepatic deletion of Pcsk9 were treated with NTS to determine the contribution of PCSK9 to the dyslipidemia of nephrotic syndrome. Patients with nephrotic syndrome showed a decrease in plasma cholesterol and plasma PCSK9 on remission of their disease (P<0.05, n=47-50). Conversely, Pod-ATTAC mice and NTS-treated mice showed hypercholesterolemia and a 7- to 24-fold induction in plasma PCSK9. The induction of plasma PCSK9 appeared to be attributable to increased secretion of PCSK9 from the hepatocyte coupled with decreased clearance. Interestingly, knockout of Pcsk9ameliorated the effects of NTS on plasma lipids. Thus, in the presence of NTS, mice lacking hepatic Pcsk9 showed a 40% to 50% decrease in plasma cholesterol and triglycerides. Moreover, the ability of NTS treatment to increase the percentage of low-density lipoprotein-associated cholesterol (from 9% in vehicle-treated Flox mice to 47% after NTS treatment), was lost in mice with hepatic deletion of Pcsk9 (5% in both the presence and absence of NTS). Podocyte damage triggers marked inductions in plasma PCSK9, and knockout of Pcsk9 ameliorates dyslipidemia in a mouse model of nephrotic syndrome. These data suggest that PCSK9 inhibitors may be beneficial in patients with nephrotic syndrome-associated hypercholesterolemia.

Proprotein convertases in atherogenesis.

The proprotein convertases subtilisin/kexin (PCSKs) are endoproteases identified as activators of precursors from hormones and peptides. On the basis of the variety of substrates and regulation in disease, they have been recognized as mediators in atherogenesis. The discovery of PCSK9, which regulates low-density lipoprotein receptor cell membrane availability, has led to a resurgence of interest in these enzymes and their function in cardiovascular diseases. Recent data demonstrate that PCSKs are expressed in human atheroma and are regulated in animal models of atherosclerosis. In animal models, inhibition of PCSKs, such as PCSK3, affects cell proliferation and migration as well as inflammation, reducing atherosclerosis. In addition, targeting PCSK9 lowers cholesterol levels and has now been demonstrated to lessen vascular lesion formation in mice. Experimentally investigated novel anti-PCSK9 strategies include genome editing and vaccination. Furthermore, studies show that PCSKs contribute to the initiation and progression of cardiometabolic risk factors, such as insulin resistance and obesity. PCSKs affect cardiovascular diseases on multiple levels, including atherosclerotic lesion formation as well as their contribution to cardiometabolic risk factors. PCSK9 is a key regulator of plasma cholesterol levels, thereby potentially affecting atherosclerosis and has rapidly emerged as a pharmacological target.