Low-density Lipoprotein Receptor Family Research Articles

Contribution of the Low-Density Lipoprotein Receptor Family to Breast Cancer Progression.

The low-density lipoprotein receptor (LDLR) family comprises 14 single-transmembrane receptors sharing structural homology and common repeats. These receptors specifically recognize and internalize various extracellular ligands either alone or complexed with membrane-spanning co-receptors that are then sorted for lysosomal degradation or cell-surface recovery. As multifunctional endocytic receptors, some LDLR members from the core family were first considered as potential tumor suppressors due to their clearance activity against extracellular matrix-degrading enzymes. LDLRs are also involved in pleiotropic functions including growth factor signaling, matricellular proteins, and cell matrix adhesion turnover and chemoattraction, thereby affecting both tumor cells and their surrounding microenvironment. Therefore, their roles could appear controversial and dependent on the malignancy state. In this review, recent advances highlighting the contribution of LDLR members to breast cancer progression are discussed with focus on (1) specific expression patterns of these receptors in primary cancers or distant metastasis and (2) emerging mechanisms and signaling pathways. In addition, potential diagnosis and therapeutic options are proposed.

Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) in the Brain and Relevance for Neuropsychiatric Disorders.

Proprotein convertase subtilisin/kexin type 9 (PCSK9) has long been studied in the liver due to its regulation of plasma low-density lipoprotein cholesterol (LDL-C) and its causal role in familial hypercholesterolemia. Although PCSK9 was first discovered in cerebellar neurons undergoing apoptosis, its function in the central nervous system (CNS) is less clear. PCSK9 has been shown to be involved in neuronal differentiation, LDL receptor family metabolism, apoptosis, and inflammation in the brain, but in vitro and in vivo studies offer contradictory findings. PCSK9 expression in the adult brain is low but is highly upregulated during disease states. Cerebral spinal fluid (CSF) PCSK9 concentrations are correlated with neural tube defects and neurodegenerative diseases in human patients. Epigenetic studies reveal that chronic alcohol use may modulate methylation of the PCSK9 gene and genetic studies show that patients with gain-of-function PCSK9 variants have higher LDL-C and an increased risk of ischemic stroke. Early safety studies of the PCSK9 inhibitors evolocumab and alirocumab, used to treat hypercholesterolemia, hinted that PCSK9 inhibition may negatively impact cognition but more recent, longer-term clinical trials found no adverse neurocognitive events. The purpose of this review is to elucidate the role of PCSK9 in the brain, particularly its role in disease pathogenesis.

Impact of LR11 as Residual Risk on Long-Term Clinical Outcomes in Patients with Coronary Artery Disease Treated with Statins after First Percutaneous Coronary Intervention.

Cardiovascular events still occur despite statin-based lipid-lowering therapy in patients with coronary artery disease (CAD). LR11, a member of the low-density lipoprotein receptor family, is a novel marker for the proliferation of intimal smooth muscle cells, which are critical to atherosclerotic plaque formation. We evaluated the impact of LR11 on long-term clinical outcomes in CAD patients treated with statins after percutaneous coronary intervention (PCI).This study included 223 consecutive CAD patients (age, 64.5 ± 9.6 years; male, 81.2%) treated with statin after first PCI between March 2003 and December 2004 at our institution. Patients were stratified to two groups according to LR11 levels (median). Composite cardiovascular disease (CVD) endpoints that included cardiovascular death, non-fatal acute coronary syndrome and non-fatal stroke were compared between groups.The rate of CVD endpoints was significantly higher in the high LR11 group (log-rank, P = 0.0029) during the median follow-up period of 2844 days. Multivariate Cox regression analysis showed that a higher LR11 level was significantly associated with adverse clinical outcomes (adjusted hazard ratio for composite CVD endpoints, 2.47; 95% confidence interval, 1.29-4.92; P = 0.006).Elevated levels of LR11 were significantly associated with long-term clinical outcomes among CAD patients treated with statins after first PCI.

Cleavage of LRP1 and increase in LRP1-ICD in ischemic brain and excitotoxic neuronal injury

Low-density lipoprotein receptor-related protein-1 (LRP1), a member of the LDL receptor family, plays important roles in endocytosis and intracellular signaling. LRP1 is processed by furin in the trans-Golgi network (TGN), becomes mature LRP1 and moves to the cell surface. Previous studies have shown that LRP1 suppresses glutamate excitotoxicity in primary cultured retinal ganglion cells. However, the pathophysiological role of LRP1 in the brain after cerebral ischemia is unclear. The purpose of this study was to investigate the pathophysiological role of LRP1 after cerebral ischemia and N-methyl-D-aspartate (NMDA)-induced neuronal injury. First, we demonstrated that LRP1 was significantly cleaved after cerebral ischemia and in NMDA-induced neuronal injury. The LRP1-intracellular domain (ICD) produced by neuronal injury was co-localized with TGN and furin. In addition, we found that furin inhibitors inhibited LRP1 cleavage and suppressed co-localization with TGN or furin. Theses findings suggest that furin-mediated LRP1 cleavage and LRP1-ICD localization are involved in ischemic neuronal injury.

Characterization of a Vitellogenin Receptor in the Bumblebee, Bombus lantschouensis (Hymenoptera, Apidae).

The vitellogenin receptor (VgR) belongs to the low-density lipoprotein receptor (LDLR) family, responsible for mediating the endocytosis of vitellogenin (Vg) into the ovaries to promote ovarian growth and oviposition. Here, we cloned and measured VgR gene expression characteristics in the bumblebee Bombus lantschouensis. RNA interference was used to validate VgR function. The results showed that the full length of the BLVgR cDNA was 5519 bp, which included a 5280 bp open reading frame encoding 1759 amino acids (AAs). Sequence alignment revealed that the protein contained 12 LDLa, 5 EGF, 2 EGF-CA and 10 LY domains. Phylogenetic analysis showed that BLVgR and the VgR of Bombus terrestris clustered together and the tree of bumblebees (Bombus) appeared as one clade next to honeybees (Apis). Transcript expression analysis showed that BLVgR was expressed in all tested tissues and showed the highest abundance in the ovaries. BLVgR expression was present in all developmental stages. However, the expression level in larvae was extremely low. In addition, the expression of BLVgR was significantly upregulated after egg laying in both workers and queens. In new emerging workers injected with 5 µg of VgR dsRNA, the expression level of BLVgR was 4-fold lower than that in the GFP dsRNA-injected group after 72 h. Furthermore, BLVgR silencing significantly reduced the number of eggs laid (3.67 ± 1.96 eggs) and delayed the first egg-laying time (16.31 ± 2.07 days) in worker microcolonies when compared to dsGFP (37.31 ± 4.09 eggs, 8.15 ± 0.22 days) and DEPC-treated water injected controls (16.42 ± 2.24 eggs, 10.00 ± 0.37 days). In conclusion, the BLVgR gene and its reproductive function were explored in the bumblebee B. lantschouensis. This gene plays an important role in egg laying time and egg number.

Development of Immature CD4+CD8+T Cells Into Mature CD4+ T Cells Requires Alpha-1 Antitrypsin as Observed by Treatment in HIV-1 Infected and Uninfected Controls.

Immune cells are, by default, migratory cells that traverse tissue for the purpose of carrying out recognition and recruitment in pathologic inflammation and infection. Members of the LDL receptor family (LDL-RFMs) interact with human leukocyte elastase on the cell surface (HLE-CS) in complex with the abundant blood protein α1proteinase inhibitor (α1PI, α1-antitrypsin, Alpha-1), a process that induces internalization of aggregated functionally-related receptors, including CD4 and the T cell antigen receptor, while simultaneously promoting cellular locomotion. We sought to determine whether augmenting α1PI blood concentration would promote the locomotion of immature T cells through the thymus and generate new CD4+ T cells. Two small clinical trials (NCT01370018, NCT01731691, https://clinicaltrials.gov) were conducted in which HIV-1 infected and uninfected individuals were augmented with α1PI and compared with placebo-treated subjects and untreated controls. Blood cell phenotypes were monitored weekly. We found that CD4/CD8 ratio was significantly increased by α1PI augmentation in both uninfected and HIV-1 infected individuals. We found that maturation of CD4+CD8+ T cells to become immunologically competent CD4+ T cells was regulated by α1PI. We propose a strategy targeting HLE-CS for treating secondary immunodeficiency for which there is currently no direct treatment. Treatment to directly elevate T cells in patients with secondary immunodeficiency, including HIV disease, can be provided by alpha-1 antitrypsin augmentation or small molecules that target HLE-CS. Because individuals infected with HIV-1 produce a monoclonal antibody, 3F5, which binds to and inactivates α1PI, a process that prevents α1PI from binding to HLE-CS, thereby blocking locomotion of immature T cells through the thymus to generate CD4+ T cells, we further propose that HIV-1 vaccination should include induction of an antibody that binds to and blocks 3F5 activity, thereby preventing AIDS in addition to the current vaccine strategy for preventing HIV-1 infection.

A Novel Approach for Generating Platelet-Delivered FVIII: Role of Transient LRP1 Expression during Megakaryopoiesis

Human platelets endocytose coagulation factor (F) V into their α-granules, in part, via low-density lipoprotein (LDL) receptor-related protein 1 (LRP1). In contrast to humans, mouse FV is endogenously expressed during megakaryopoiesis and stored in α-granules. The FV-related coagulation factor FVIII is not endogenously expressed in megakaryocytes (Mks) and thought not to be endocytosed by human or murine Mks/platelets. The lack of FVIII endocytosis is surprising as LRP1 on multiple cell types is involved in FVIII uptake and clearance. We and others have shown that FVIII can be ectopically expressed during human or murine megakaryopoiesis and stored in α-granules. These platelets are effective in the delivery of FVIII to sites of vascular injury and improve outcome in hemophilia A (HA) mice even in the presence of circulating inhibitors. Thus, it has been proposed that lentiviral bone marrow gene therapy to ectopically express FVIII during megakaryopoiesis may be a curative strategy especially for patients with HA and intractable inhibitors. However, we have shown that pFVIII has a toxic effect on Mks during intracellular processing in the endoplasmic reticulum/Golgi, limiting platelet yield and pFVIII levels. We have recently shown that exogenous FV can be taken up by in vitro differentiated CD34+- and by induced pluripotent stem cell (iPSC)-derived Mks and asked if the same can be done with FVIII. We found that Mks can take up full-length FVIII (Advate) (Fig. 1A), B-domainless (BD) FVIII (Xyntha, not shown) and BD FVIIIR1645H (not shown), a FVIII mutant we have shown is particularly effective when released by platelets. Uptake is half maximum at 0.25 IU/ml following overnight incubation. Endocytosed FVIII colocalizes with labeled fibrinogen uptake (Fig. 1A), supporting its localization to α-granules, and this FVIII uptake can be blocked by receptor-associated protein (RAP), a blocker of LDL receptor family members, including LRP1 (Fig. 1A) or by including FVIII's carrier protein von Willebrand factor (VWF) (Fig. 1B). To test the biological efficacy of endocytosed pFVIII, we took advantage of our previous studies showing that infused Mks into mice release highly functional platelets after becoming entrapped in the lungs. To focus our studies on the released human platelets and the hemostatic efficacy of the endocytosed pFVIII, we used immunodeficient NOD-scid IL2rgnull (NSG) mice that were also FVIII-deficient and that only expressed mutant VWF that binds human, but not mouse, platelet glycoprotein Ib/IX (VWFR1326H) (N/8/V mice). We infused 1x106 human FVIII-endocytosed Mks into these N/8/V mice resulting in ~1-10% being human platelets in recipient mice. We studied hemostatic efficacy by rotational thromboelastography (ROTEM) and demonstrated that the in vivo-released FVIII from released human platelets within the N/8/V blood corrected hemostasis in this system (Fig. 1C). These FVIII-containing platelets fully corrected clotting as well in a FeCl3 carotid artery injury model (Fig. 1D). In summary, we found that in vitro-grown human Mks can endocytose FVIII from the media into their α-granules in sufficient amounts to have potential clinical application in the care of HA patients. This endocytosis is likely via LRP1. FVIII is not found normally in platelets likely because of a combination of the following: 1) in plasma, FVIII it is bound to VWF, 2) circulating platelets also lack LRP1, and 3) in the marrow, there is little or no free FVIII for endocytosis by LRP1-positive Mks. We propose that endocytosed FVIII by Mks can be an important clinical application of commercial, in vitro-grown Mks for patients with HA and inhibitors who need supplemental long-lasting, hemostatic support to their emicizumab without the thrombotic risks of FVIII-bypassing agents. Disclosures Sabatino: Spark Therapeutics: Patents & Royalties. Camire:Pfizer: Research Funding.

A Novel Platelet-Targeting Fibrinolytic Strategy: Endocytosed Urokinase By Megakaryocytes Is Stored in α-Granules and Is Functional In Vivo in a Murine Model of Thrombosis

We have been interested in developing fibrinolytic agents that have a prolonged half-life and can selectively prevent new thrombi from forming without destabilizing established hemostatic clots. We believe that platelet-targeting of urokinase plasminogen activator (uPA) might be able to achieve this goal. Two approaches had been tried in the past: In the first, we had generated chimeric drugs consisting of a platelet-targeting scFvs fused to a thrombin activatable low molecular weight (LMW) uPA (uPA-T). Infused scFv/uPA-T bound to circulating platelets that targeted the fusion within nascent thrombi where significant amounts of thrombin are generated to activate surface-bound scFv/uPA-T. In contrast, mature thrombi are spared because scFv/uPA-T platelets are not activated on the "shell", nor do they penetrate the "core" where thrombin might be present. Murine studies affirmed αIIbβ3-directed scFv/uPA-T provided thromboprophylaxis, but therapeutic doses caused significant thrombocytopenia in murine and baboon models. We therefore considered a second approach: ectopic storage of uPA during megakaryopoiesis. We found that scuPA was stored in platelet α-granules of transgenic mice that ectopically express single-chain uPA (scuPA) and did not cause systemic fibrinolysis. Infusion of such "scuPA platelets" into wildtype mice was highly effective at preventing new thrombi from developing. We now wish to develop this strategy further by taking advantage of ongoing efforts by others to generate in vitro-grown megakaryocytes (Mks) and platelets that can be modified to express uPA near the point-of-care and then infused into patients, bypassing the need to establish uPA-expressing hematopoietic cell lines. We have previously shown that Mks express low-density lipoprotein (LDL) receptor-related protein 1 (LRP1) during their maturation, whereas the platelets that are released do not. We now asked whether in vitro-grown Mks beginning with CD34+ hematopoietic cells would endocytose uPA as seen in other cell types. We show that Mks internalize and store scuPA (scu-Mks, Fig. 1A), as well as LMW uPA and uPA-T (not shown) after overnight incubation. Endocytosed uPA is found within membrane bound structures that partly colocalize with von Willebrand factor (VWF)-positive granules, suggesting uPA is sorted to α-granules (Fig. 1A). Uptake is blocked by receptor-associated protein (RAP), which inhibits endocytosis by LDL receptor family members, including LRP1. We then studied whether platelets with endocytosed scuPA (scuPA-Plts) prevent nascent thrombus development in immunodeficient NOD-scid IL2rγnull (NSG) mice that are also homozygous for VWFR1326H (a single amino acid substitution that switches species selectivity of VWF so that it binds human platelet glycoprotein (GP) Ib/IX receptor rather than mouse GPIb/IX). These mice show a mild bleeding diathesis in a Rose Bengal photochemical carotid artery injury model unless they are infused with human Mks, which we have shown go on to release functional platelets in the recipient animal in its pulmonary capillary bed over the ensuing several hours (Fig. 1B). Thus, when 106 Mks not exposed to uPA were infused so that ~1-10% of circulating platelets were human, thrombi developed in this model; however similar infusion of scuPA-Mks did not occlude (Fig. 1B). In tail clip studies in the same genotypic mice, where the mice were first corrected with human platelets (Fig. 1C) followed 10 min later by scuPA-Mks, rebleeding did not develop when given a similar dose of scuPA-Mks that prevented thrombosis in the photochemical injury model. These studies suggest that Mks internalize biologically relevant concentrations of uPA through a process likely to involve LRP1. Whether ex vivo loading of Mks with uPA can serve as model for point-of-care therapeutics for thromboprophylaxis and diverse other hematologic and non-hematologic indications should be explored. Disclosures No relevant conflicts of interest to declare.

Cellular Uptake and Clearance of Oxidatively-modified Apolipoprotein E3 by Cerebral Cortex Endothelial Cells.

Apolipoprotein E3 (apoE3) plays a critical role in the metabolism of lipoproteins and lowers plasma lipid levels by serving as a ligand for the low-density lipoprotein receptor (LDLr) family of proteins and by promoting macrophage cholesterol efflux. The current study examines the effect of acrolein (an endogenously generated metabolite and an environmental pollutant) modification on the structure and function of apoE3. Acrolein modification was confirmed in Western blots by reactivity with acrolein–lysine-specific antibody and by the presence of oligomeric species due to cross-linking. LC-MS/MS analysis revealed modification of 10 out of 12 lysines in apoE3, with Nε-(3-methylpyridinium)-lysine being the predominant form of modification, and Lys75 being a ‘hot spot’ in terms of susceptibility to oxidation. Circular dichroism spectroscopy showed no major change in overall secondary structure compared to unmodified apoE3. Reconstituted high density lipoprotein (HDL) bearing acrolein modified apoE3 showed loss of binding to soluble LDLr; however, incubation with mouse endothelioma bEnd.3 cells showed that it was internalized. Incubation with excess LDL did not abolish cellular uptake of acrolein modified apoE3, suggesting alternative mechanism(s) not involving LDLr. Incubation with anti-CD36 antibody did not show a decrease in internalization while incubation with anti- lectin-like oxidized LDL receptor 1 (LOX1) showed partial internalization. However, incubation with anti-scavenger receptor class B type I (SRB1) antibody abolished internalization of acrolein modified apoE3. Taken together, our studies suggest that acrolein modification of apoE3 at lysine residues leads to increase in net negative charge, and as a consequence, results in clearance by LOX1 and SRB1 on endothelial cells. Overall, oxidative modification of apoE3 likely impairs its role in regulating plasma cholesterol homeostasis, eventually leading to lipid disorders.

Effects of oxygen-glucose deprivation (OGD) on barrier properties and mRNA transcript levels of selected marker proteins in brain endothelial cells/astrocyte co-cultures.

Ischemic stroke has been shown to induce breakdown of the blood-brain barrier, although these changes are not fully characterized. Oxygen-glucose deprivation (OGD) has been used to investigate the effects of ischemia in cultured brain capillary endothelial cells, however this involves a change of medium which in itself may affect the cells. The aim of the present study was to investigate the effect of OGD and simple medium exchange followed by 48 h of reperfusion on barrier properties of primary bovine endothelial cells co-cultured with rat astrocytes. Barrier properties were evaluated by transendothelial electrical resistance measurements, passive permeability of flux markers, RT-qPCR and immunocytochemistry. Both OGD and simple medium exchange caused an increase in endothelial monolayer permeability. This correlated with reduced transcript levels of a number of tight junction and tight junction-associated proteins (claudin-1, claudin-5, occludin, ZO-1, tricellulin, marveld3 and PECAM-1), as well as with altered transcript level of several transporters and receptors (GLUT-1, HB-EGF, InsR, TfR, two members of the low density lipoprotein receptor family, LDLR and LRP-1, and the efflux transporter BCRP). In contrast, effects induced specifically by OGD were transient de-localization of claudin-5 from the junction zone, increased InsR localization at the plasma membrane and transient downregulation of MRP-1 and P-gp transcript levels. In conclusion, OGD caused changes in claudin-5 and InsR localization, as well as in MRP-1 and P-gp transcript levels. Our results however also indicated that medium exchange alone caused changes in functional barrier properties and expression levels of wide range of proteins.

Silencing the Very Low-density Lipoprotein Receptor (VLDLR) Prevents Obesity Associated with Excess Lipid Deposition (P21-040-19)

ObjectivesObesity is associated with an insulin resistant state, characterized by abnormalities in lipid metabolism, a leading cause of morbidity and mortality in cardiovascular diseases (CVD). Very low-density lipoprotein receptor (VLDLR), a member of the LDL receptor family, binds and increases the catabolism of apolipoprotein E triglyceride-rich lipoproteins. Although VLDLR is highly expressed in the heart, its role in obesity associated lipotoxicity is not well understood. MethodsIn the current study, lean WT, VLDLR-deficient (VLDLR−/−), genetically obese leptin-deficient (Lepob/ob), and leptin–VLDLR double-null (Lepob/ob/VLDLR−/−) mice were used to determine the impact of VLDLR deficiency on obesity-induced cardiac lipotoxicity. ResultsThe results showed that insulin sensitivity and glucose uptake were reduced in the hearts of Lepob/ob mice, and at the same time, VLDLR expression was upregulated and associated with increased VLDL uptake resulting in excess lipid deposition. These changes were accompanied by upregulation of cardiac NADPH oxidase (Nox) expression and increased production of Nox-dependent superoxides. Silencing the VLDLR in Lepob/ob mice reduced VLDL uptake and prevented excess lipid deposition. Moreover, VLDLR deficiency reduced superoxide overproduction and normalized glucose uptake. In isolated cardiomyocytes, VLDLR deficiency prevented VLDL-mediated induction of NOx activity and superoxide overproduction while improving insulin sensitivity and glucose uptake. An important observation showed that Lepob/ob/VLDLR−/− mice compared to Lepob/ob mice, had significantly improved heart performance and energetic reserves. ConclusionsThese findings suggest that that when VLDLR is silenced (deficiency), lipid deposition is also reduced, preventing cardiac lipotoxicity in obesity. In addition, the effects may be linked to the role of VLDLR on VLDL uptake, which triggers a cascade of events leading to insulin resistance and superoxide overproduction. Funding SourcesInstitutional Support.Howard University, Washington DC 20059Hackensack University Medical Center, NJ 07601

Clathrin and clathrin adaptor AP-1 control apical trafficking of megalin in the biosynthetic and recycling routes.

Megalin (gp330, LRP-2) is a protein structurally related to the low-density lipoprotein receptor family that displays a large luminal domain with multiligand binding properties. Megalin localizes to the apical surface of multiple epithelia, where it participates in endocytosis of a variety of ligands performing roles important for development or homeostasis. We recently described the apical recycling pathway of megalin in Madin–Darby canine kidney (MDCK) cells and found that it is a long-lived, fast recycling receptor with a recycling turnover of 15 min and a half-life of 4.8 h. Previous work implicated clathrin and clathrin adaptors in the polarized trafficking of fast recycling basolateral receptors. Hence, here we study the role of clathrin and clathrin adaptors in megalin’s apical localization and trafficking. Targeted silencing of clathrin or the γ1 subunit of clathrin adaptor AP-1 by RNA interference in MDCK cells disrupted apical localization of megalin, causing its redistribution to the basolateral membrane. In contrast, silencing of the γ2 subunit of AP-1 had no effect on megalin polarity. Trafficking assays we developed using FM4-HA-miniMegalin-GFP, a reversible conditional endoplasmic reticulum–retained chimera, revealed that clathrin and AP-1 silencing disrupted apical sorting of megalin in both biosynthetic and recycling routes. Our experiments demonstrate that clathrin and AP-1 control the sorting of an apical transmembrane protein.

Low-Density Lipoprotein Particle Size Subfractions and Cerebral Amyloidosis.

Cerebral beta-amyloidosis (CA) is a condition in which amyloid-β (Aβ) proteins are deposited in the cerebral cortex and is a predictor of Alzheimer's disease (AD). The Aging Brain Study (ABS) investigated risk factors for CA in persons with diabetes and dyslipidemia. In the ABS, we identified that greater levels of LDL cholesterol and lower levels of HDL cholesterol were associated with increased CA. LDL particles comprise multiple species of varying size, density, and protein composition. For example, within a lipoprotein profile characteristic for persons with obesity and diabetic dyslipidemia, larger LDL particles have a greater ApoE to ApoB ratio, enhancing their binding affinity to LDL receptors. The goal of this study was to identify LDL particles that associate with CA in ABS. LDL particle size fractions were measured by ion mobility in plasma samples of 58 participants (40 women and 18 men). CA was assessed using Pittsburgh Compound B index-Positron Emission Tomography (PiB-PET) imaging. Among the LDL subfractions, greater plasma levels of large LDL particles were significantly associated with greater cerebral amyloidosis and lower hippocampal volumes independent of LDL cholesterol or triglyceride levels. Since Aβ is cleared by the LDL receptor family, such as lipoprotein-like receptor 1 (LRP1), one potential mechanism for our findings is competition between ApoE enriched larger LDL particles and brain-derived Aβ on hepatic Aβ clearance and degradation. We conclude that assessing larger LDL particles in persons with atherogenic dyslipidemia may provide a mechanistic biomarker for the extent of CA.

The Roles of Low-Density Lipoprotein Receptor-Related Proteins 5, 6, and 8 in Cancer: A Review.

Low-density lipoprotein receptor (LDLR) has been an object of research since the 1970s because of its role in various cell functions. The LDLR family members include LRP5, LRP6, and LRP8. Even though LRP5, 6, and 8 are in the same family, intriguingly, these three proteins have various roles in physiological events, as well as in regulating different mechanisms in various kinds of cancers. LRP5, LRP6, and LRP8 have been shown to play important roles in a broad panel of cancers. LRP5 is highly expressed in many tissues and is involved in the modulation of glucose-induced insulin secretion, bone development, and cholesterol metabolism, as well as cancer progression. Recently, LRP5 has also been shown to play a role in chondroblastic subtype of osteosarcoma (OS) and prostate cancer and also in noncancer case such as osteoporosis. LRP6, which has been previously discovered to share the same structures as LRP5, has also been associated with many cancer progressions such as human triple negative breast cancer (TNBC), primary chronic lymphocytic leukemia (CLL), nonsmall cell lung cancer (NSCL), lung squamous cell carcinoma (LSCC), and hepatocellular carcinoma (HCC). In addition to its role in cancer progression, LRP8 (apolipoprotein E receptor 2 [APOER2]) has also been demonstrated to regulate canonical Wnt/β-catenin signaling pathway whereby this pathway plays a role in cell migration and development. Therefore, this review aimed to elucidate the role of LRP 5, 6, and 8 in regulating the cancer progression.

Low Density Receptor-Related Protein 1 Interactions With the Extracellular Matrix: More Than Meets the Eye.

The extracellular matrix (ECM) is a biological substrate composed of collagens, proteoglycans and glycoproteins that ensures proper cell migration and adhesion and keeps the cell architecture intact. The regulation of the ECM composition is a vital process strictly controlled by, among others, proteases, growth factors and adhesion receptors. As it appears, ECM remodeling is also essential for proper neuronal and glial development and the establishment of adequate synaptic signaling. Hence, disturbances in ECM functioning are often present in neurodegenerative diseases like Alzheimer’s disease. Moreover, mutations in ECM molecules are found in some forms of epilepsy and malfunctioning of ECM-related genes and pathways can be seen in, for example, cancer or ischemic injury. Low density lipoprotein receptor-related protein 1 (Lrp1) is a member of the low density lipoprotein receptor family. Lrp1 is involved not only in ligand uptake, receptor mediated endocytosis and lipoprotein transport—functions shared by low density lipoprotein receptor family members—but also regulates cell surface protease activity, controls cellular entry and binding of toxins and viruses, protects against atherosclerosis and acts on many cell signaling pathways. Given the plethora of functions, it is not surprising that Lrp1 also impacts the ECM and is involved in its remodeling. This review focuses on the role of Lrp1 and some of its major ligands on ECM function. Specifically, interactions with two Lrp1 ligands, integrins and tissue plasminogen activator are described in more detail.

Systemic peptide mediated delivery of an siRNA targeting α-syn in the CNS ameliorates the neurodegenerative process in a transgenic model of Lewy body disease.

Neurodegenerative disorders of the aging population are characterized by progressive accumulation of neuronal proteins such as α-synuclein (α-syn) in Parkinson's Disease (PD) and Amyloid ß (Aß) and Tau in Alzheimer's disease (AD) for which no treatments are currently available. The ability to regulate the expression at the gene transcription level would be beneficial for reducing the accumulation of these proteins or regulating expression levels of other genes in the CNS. Short interfering RNA molecules can bind specifically to target RNAs and deliver them for degradation. This approach has shown promise therapeutically in vitro and in vivo in mouse models of PD and AD and other neurological disorders; however, delivery of the siRNA to the CNS in vivo has been achieved primarily through intra-cerebral or intra-thecal injections that may be less amenable for clinical translation; therefore, alternative approaches for delivery of siRNAs to the brain is needed. Recently, we described a small peptide from the envelope protein of the rabies virus (C2-9r) that was utilized to deliver an siRNA targeting α-syn across the blood brain barrier (BBB) following intravenous injection. This approach showed reduced expression of α-syn and neuroprotection in a toxic mouse model of PD. However, since receptor-mediated delivery is potentially saturable, each allowing the delivery of a limited number of molecules, we identified an alternative peptide for the transport of nucleotides across the BBB based on the apolipoprotein B (apoB) protein targeted to the family of low-density lipoprotein receptors (LDL-R). We used an 11-amino acid sequence from the apoB protein (ApoB11) that, when coupled with a 9-amino acid arginine linker, can transport siRNAs across the BBB to neuronal and glial cells. To examine the value of this peptide mediated oligonucleotide delivery system for PD, we delivered an siRNA targeting the α-syn (siα-syn) in a transgenic mouse model of PD. We found that ApoB11 was effective (comparable to C2-9r) at mediating the delivery of siα-syn into the CNS, co-localized to neurons and glial cells and reduced levels of α-syn protein translation and accumulation. Delivery of ApoB11/siα-syn was accompanied by protection from degeneration of selected neuronal populations in the neocortex, limbic system and striato-nigral system and reduced neuro-inflammation. Taken together, these results suggest that systemic delivery of oligonucleotides targeting α-syn using ApoB11 might be an interesting alternative strategy worth considering for the experimental treatment of synucleinopathies.

The genetic and epigenetic association of LDL Receptor Related Protein 1B (LRP1B) gene with childhood obesity

Low-density lipoprotein Receptor Related Protein 1B (LRP1B) is homologous to the gigantic lipoprotein receptor-related protein 1 that belongs to the family of Low-density lipoprotein receptors. Previous genetic association studies of the LRP1B gene have shown its genetic association with obesity. Through exome sequencing of the LRP1B gene from a childhood severe obesity cohort (n = 692), we found novel single nucleotide polymorphism (rs431809) in intron 4, which has been significantly correlated with both body mass index (BMI) and waist-hip-ratio (WHR). Three methylations of CpG sites (cg141441481, cg01852095 and cg141441470) in the same intron were also significantly correlated with BMI and WHR. All CpG methylations had bimodal patterns, and were dependent on rs431809 genotypes. The genetic influences of obesity on the LRP1B gene may be linked to the interplay of CpG methylations in the same intron. Heritability of SNP interacts with epigenetic crosstalk in LRP1B. Genetic and epigenetic crosstalk of LRP1B gene may be implicated in the prevention and therapeutic approach to childhood obesity.

PCSK9 in Haemostasis and Thrombosis: Possible Pleiotropic Effects of PCSK9 Inhibitors in Cardiovascular Prevention.

Since increased cholesterol levels are crucial in determining the development of atheroma, their reduction represents a mainstay in primary and secondary cardiovascular prevention. The most recent spectacular advancement in cholesterol-lowering therapy is represented by proprotein convertase subtilisin/kexin type-9 (PCSK9) inhibitors. Although their benefit over currently available treatments has been ascribed primarily to their strong low-density lipoprotein (LDL)-cholesterol reducing action, several clues suggest that PCSK9 inhibitors may also influence platelet function and blood coagulation. PCSK9 knockout mice develop less venous and arterial thrombosis and show reduced in vivo platelet activation upon arterial injury. In patients with acute coronary syndromes (ACSs) treated with P2Y12 inhibitors, a direct association between PCSK9 serum levels and residual platelet reactivity was found. A direct correlation between urinary excretion of 11-dehydro-thromboxane-B2, a marker of in vivo platelet activation, and circulating PCSK9 levels was reported in patients with atrial fibrillation. Moreover, recombinant human PCSK9 added in vitro to human platelets potentiated activation induced by weak agonists. Finally, blood clotting factor VIII (FVIII), which is associated with stroke and ACS risk, is cleared from the circulation by members of the LDL receptor (LDLR) family. Given that PCSK9 degrades LDLR, it is conceivable that PCSK9 inhibitors by enhancing the expression of LDLR may slightly decrease circulating FVIII, in this way contributing to the prevention of cardiovascular events. This review aims to discuss the possible and hypothetical interactions between PCSK9 and the haemostatic system and to examine the possible pleiotropic effects of PCSK9 inhibitors in cardiovascular prevention.

Soluble LR11 competes with amyloid β in binding to cerebrospinal fluid–high-density lipoprotein

BackgroundLR11 is a member of the low-density lipoprotein (LDL) receptor family with high expression in neurons. Some cell surface LR11 is cleaved and secreted into the cerebrospinal fluid (CSF) as soluble LR11 (sLR11). Patients with Alzheimer's disease (AD), particularly apolipoprotein E4 carriers, have high CSF–sLR11 and low CSF–amyloid β (Aβ) concentrations. Therefore, we assessed whether sLR11 is bound to CSF–high-density lipoprotein (HDL) and whether sLR11 competes with Aβ in binding to apoE in CSF–HDL. MethodsWe measured CSF–sLR11 concentrations (50 controls and 16 patients with AD) using enzyme immunoassay. sLR11 and apoE distribution in the CSF was evaluated using non-denaturing two-dimensional gel electrophoresis (N–2DGE). ApoE bound to sLR11 or Aβ was identified using co-immunoprecipitation assay. ResultsCSF–sLR11 concentrations were higher in patients with AD than controls (adjusted for sLR11 using phospholipid). N–2DGE analysis showed that sLR11 and Aβ comigrated with a large apoE-containing CSF–HDL. Moreover, fewer apoE was bound to Aβ when a higher amount of apoE was bound to sLR11 in patients with AD who presented with ε4/4. ConclusionsLR11 binds to CSF–HDL and competes with Aβ in binding to apoE in CSF–HDL, indicating that sLR11 affects Aβ clearance via CSF–HDL.

Apoprotein E and Reverse Cholesterol Transport.

Apoprotein E (apoE) is a multifunctional protein. Its best-characterized function is as a ligand for low-density lipoprotein (LDL) receptor family members to mediate the clearance of apoB-containing atherogenic lipoproteins. Among its other functions, apoE is involved in cholesterol efflux, especially from cholesterol-loaded macrophage foam cells and other atherosclerosis-relevant cells, and in reverse cholesterol transport. Reverse cholesterol transport is a mechanism by which excess cellular cholesterol is transported via lipoproteins in the plasma to the liver where it can be excreted from the body in the feces. This process is thought to have a role in the attenuation of atherosclerosis. This review summarizes studies on the role of apoE in cellular cholesterol efflux and reverse cholesterol transport and discusses the identification of apoE mimetic peptides that may promote these pathways.