Molecular and cellular function of the proprotein convertase subtilisin/kexin type 9 (PCSK9).
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ABSTRACT:
SUBMITTER: Schulz R
PROVIDER: S-EPMC4298671 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:BackgroundPCSK9 regulates low-density lipoprotein cholesterol (LDLc) level and has been implicated in hypercholesterolemia. Aberrant plasma lipid profile is often associated with various cancers. Clinically, the relationship between altered serum lipid level and hepatocellular carcinoma (HCC) has been documented; however, the underlying cause and implications of such dyslipidemia remain unclear.MethodsThe present study includes the use of HepG2 tumor xenograft model to study the potential role of glucose (by providing 15% glucose via drinking water) in regulating PCSK9 expression and associated hypercholesterolemia. To support in vivo findings, in vitro approaches were used by incubating HCC cells in culture medium with different glucose concentrations or treating the cells with glucose uptake inhibitors. Impact of hypercholesterolemia on chemotherapy was demonstrated by exogenously providing LDLc followed by appropriate in vitro assays.ResultsWe observed that serum and hepatic PCSK9 level is decreased in mice which were provided with glucose containing water. Interestingly, serum and tumor PCSK9 level was upregulated in HepG2-tumor-bearing mice having access to water containing glucose. Additionally, elevated LDLc is detected in sera of these mice. In vitro studies indicated that PCSK9 expression was increased by high glucose availability with potential involvement of reactive oxygen species (ROS) and sterol regulatory element binding protein-1 (SREBP-1). Furthermore, it is also demonstrated that pre-treatment of cells with LDLc diminishes cytotoxicity of sorafenib in HCC cells.ConclusionTaken together, these results suggest a regulation of PCSK9 by high glucose which could contribute, at least partly, towards understanding the cause of hypercholesterolemia in HCC and its accompanied upshots in terms of altered response of HCC cells towards cancer therapy.
| S-EPMC6201570 | biostudies-literature
Project description:Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a soluble protein that directs membrane-bound receptors to lysosomes for degradation. In the most studied example of this, PCSK9 binding leads to the degradation of low density lipoprotein receptor (LDLR), significantly affecting circulating LDL-C levels. The mechanism mediating this degradation, however, is not completely understood. We show here that LDLR facilitates PCSK9 interactions with amyloid precursor like protein 2 (APLP2) at neutral pH leading to PCSK9 internalization, although direct binding between PCSK9 and LDLR is not required. Moreover, binding to APLP2 or LDLR is independently sufficient for PCSK9 endocytosis in hepatocytes, while LDL can compete with APLP2 for PCSK9 binding to indirectly mediate PCSK9 endocytosis. Finally, we show that APLP2 and LDLR are also required for the degradation of another PCSK9 target, APOER2, necessitating a general role for LDLR and APLP2 in PCSK9 function. Together, these findings provide evidence that PCSK9 has at least two endocytic epitopes that are utilized by a variety of internalization mechanisms and clarifies how PCSK9 may direct proteins to lysosomes.
| S-EPMC4408062 | biostudies-literature
Project description:Lipoprotein apheresis (LA) reduces low-density lipoprotein (LDL) levels in patients with severe familial hypercholesterolemia (FH). We have recently reported that >30% of plasma proprotein convertase subtilisin/kexin 9 (PCSK9) is bound to LDL, thus we predicted that LA would also reduce plasma PCSK9 levels by removing LDL.Pre- and post-apheresis plasma from 6 patients with familial hypercholesterolemia on 3 consecutive treatment cycles was used to determine changes in PCSK9 levels.LA drastically reduced plasma LDL (by 77 ± 4%). Concomitantly, PCSK9 levels fell by 52 ± 5%, strongly correlating with the LDL drop (P=0.0322; r(2)=0.26), but not with decreases in triglyceride (49 ± 13%) or high-density lipoprotein levels (18 ± 2%). Levels of albumin, creatinine, and CK-MB did not show significant changes after LA. Similar to LDL, PCSK9 levels returned to pretreatment values between cycles (2-week intervals). Fractionation of pre- and post-apheresis plasma showed that 81 ± 11% of LDL-bound PCSK9 and 48 ± 14% of apolipoprotein B-free PCSK9 were removed. Separation of whole plasma, purified LDL, or the apolipoprotein B-free fraction through a scaled-down, experimental dextran sulfate cellulose beads column produced similar results.Our results show, for the first time, that modulation of LDL levels by LA directly affects plasma PCSK9 levels, and suggest that PCSK9 reduction is an additional benefit of LA. Because the loss of PCSK9 could contribute to the LDL-lowering effect of LA, then (1) anti-PCSK9 therapies may reduce frequency of LA in patients currently approved for therapy, and (2) LA and anti-PCSK9 therapies may be used synergistically to reduce treatment burden.
| S-EPMC3939022 | biostudies-literature
Project description:PCSK9 (proprotein convertase subtilisin/kexin type 9) has emerged as a novel therapeutic target for hypercholesterolemia due to its LDL receptor (LDLR)-reducing activity. Although its structure has been solved, the lack of a detailed understanding of the structure-function relation hinders efforts to develop small molecule inhibitors. In this study, we used mutagenesis and transfection approaches to investigate the roles of the prodomain (PD) and the C-terminal domain (CD) and its modules (CM1-3) in the secretion and function of PCSK9. Deletion of PD residues 31-40, 41-50, or 51-60 did not affect the self-cleavage, secretion, or LDLR-degrading activity of PCSK9, whereas deletion of residues 61-70 abolished all of these functions. Deletion of the entire CD protein did not impair PCSK9 self-cleavage or secretion but completely abolished LDLR-degrading activity. Deletion of any one or two of the CD modules did not affect self-cleavage but influenced secretion and LDLR-reducing activity. Furthermore, in cotransfection experiments, a secretion-defective PD deletion mutant (?PD) was efficiently secreted in the presence of CD deletion mutants. This was due to the transfer of PD from the cotransfected CD mutants to the ?PD mutant. Finally, we found that a discrete CD protein fragment competed with full-length PCSK9 for binding to LDLR in vitro and attenuated PCSK9-mediated hypercholesterolemia in mice. These results show a previously unrecognized domain interaction as a critical determinant in PCSK9 secretion and function. This knowledge should fuel efforts to develop novel approaches to PCSK9 inhibition.
| S-EPMC3234880 | biostudies-other
Project description: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.
| S-EPMC7303295 | biostudies-literature
Project description:BACKGROUND:Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a hepatic enzyme that regulates circulating low-density lipoprotein (LDL) cholesterol levels by binding to LDL receptors (LDLR) and promoting their degradation. Although PCSK9 inhibitors were shown to reduce the risk of cardiovascular disease, a warning was issued concerning their possible impact on cognitive functions. In Alzheimer's disease (AD), it is believed that cognitive impairment is associated with cholesterol metabolism alterations, which could involve PCSK9. The main objective of this study is to determine if PCSK9 plays a significant role in the pre-symptomatic phase of the disease when the pathophysiological markers of AD unfolds and, later, when cognitive symptoms emerge. METHODS AND FINDINGS:To test if PCSK9 is associated with AD pathology, we measured its expression levels in 65 autopsy confirmed AD brains and 45 age and gender matched controls. Messenger ribonucleic acid (mRNA) were quantified using real-time polymerase chain reaction (RT-PCR) and protein levels were quantified using enzyme-linked immunosorbent assay (ELISA). PCSK9 was elevated in frontal cortices of AD subjects compared to controls, both at the mRNA and protein levels. LDLR protein levels were unchanged in AD frontal cortices, despite and upregulation at the mRNA level. To verify if PCSK9 dysregulation was observable before the onset of AD, we measured its expression in the cerebrospinal fluid (CSF) of 104 "at-risk" subjects and contrasted it with known apolipoproteins levels and specific AD biomarkers using ELISAs. Positive correlations were found between CSF PCSK9 and apolipoprotein E (APOE), apolipoprotein J (APOJ or CLU), apolipoprotein B (APOB), phospho Tau (pTau) and total Tau. To investigate if PCSK9 levels were driven by genetic variants, we conducted an expression quantitative trait loci (eQTL) study using bioinformatic tools and found two polymorphisms in strong association. Further investigation of these variants in two independent cohorts showed a female specific association with AD risk and with CSF Tau levels in cognitively impaired individuals. CONCLUSIONS:PCSK9 levels differ between control and AD brains and its protein levels correlate with those of other lipoproteins and AD biomarkers even before the onset of the disease. PCSK9 regulation seems to be under tight genetic control in females only, with specific variants that could predispose to increased AD risk.
| S-EPMC6705826 | biostudies-literature
Project description:BackgroundThe relationship between cholesterol levels and risk of venous thromboembolism (VTE) is uncertain. We set out to determine the effect of PCSK9 (proprotein convertase subtilisin/kexin type 9) inhibition on the risk of VTE, explore potential mechanisms, and examine the efficacy in subgroups with clinically and genetically defined risk.MethodsWe performed a post hoc analysis of the FOURIER trial (Further Cardiovascular Outcomes Research With PCSK9 Inhibition in Subjects With Elevated Risk) testing whether evolocumab reduces the risk of VTE events (deep venous thrombosis or pulmonary embolism). Data from FOURIER and ODYSSEY OUTCOMES (Evaluation of Cardiovascular Outcomes After an Acute Coronary Syndrome During Treatment with Alirocumab) were then combined in a meta-analysis to assess the class effect of PCSK9 inhibition on the risk of VTE. We also analyzed baseline lipids in FOURIER to investigate potential mechanisms explaining the reduction in VTE with evolocumab. Last, an exploratory genetic analysis was performed in FOURIER to determine whether a VTE polygenic risk score could identify high-risk patients who would derive the greatest VTE reduction from evolocumab.ResultsIn FOURIER, the hazard ratio (HR) for VTE with evolocumab was 0.71 (95% CI, 0.50-1.00; P=0.05), with no effect in the 1st year (HR, 0.96 [95% CI, 0.57-1.62]) but a 46% reduction (HR, 0.54 [95% CI, 0.33-0.88]; P=0.014) beyond 1 year. A meta-analysis of FOURIER and ODYSSEY OUTCOMES demonstrated a 31% relative risk reduction in VTE with PCSK9 inhibition (HR, 0.69 [95% CI, 0.53-0.90]; P=0.007). There was no relation between baseline low-density lipoprotein cholesterol levels and magnitude of VTE risk reduction. In contrast, in patients with higher baseline lipoprotein(a) (Lp[a]) levels, evolocumab reduced Lp(a) by 33 nmol/L and risk of VTE by 48% (HR, 0.52 [95% CI, 0.30-0.89]; P=0.017), whereas, in patients with lower baseline Lp(a) levels, evolocumab reduced Lp(a) by only 7 nmol/L and had no effect on VTE risk (Pinteraction 0.087 for HR; Pheterogeneity 0.037 for absolute risk reduction). Modeled as a continuous variable, there was a significant interaction between baseline Lp(a) concentration and magnitude of VTE risk reduction (Pinteraction=0.04). A polygenic risk score identified patients who were at >2-fold increased risk for VTE and who derived greater relative (Pinteraction=0.04) and absolute VTE reduction (Pheterogeneity=0.009) in comparison with those without high genetic risk.ConclusionsPCSK9 inhibition significantly reduces the risk of VTE. Lp(a) reduction may be an important mediator of this effect, a finding of particular interest given the ongoing development of potent Lp(a) inhibitors.
| S-EPMC7469753 | biostudies-literature
Project description:Niemann-Pick disease, type C1, is a cholesterol storage disease where unesterified cholesterol accumulates intracellularly. In the cerebellum this causes neurodegeneration of the Purkinje neurons that die in an anterior-to-posterior and time-dependent manner. This results in cerebellar ataxia as one of the major outcomes of the disease. Proprotein convertase subtilisin/kexin type 9 (PCSK9) plays a significant role in the regulation of serum cholesterol levels by modulating LDL receptor levels on peripheral tissues. In the central nervous system, PCSK9 may have a similar effect on the closely related VLDL and ApoE2 receptors to regulate brain cholesterol. In addition, regulation of VLDLR and ApoER2 by PCSK9 may contribute to neuronal apoptotic pathways through Reelin, the primary ligand of VLDLR and ApoER2. Defects in reelin signaling results in cerebellar dysfunction leading to ataxia as seen in the Reeler mouse. Our recent findings that Pcsk9 is expressed ~8-fold higher in the anterior lobules of the cerebellum compared to the posterior lobule X, which is resistant to neurodegeneration, prompted us to ask whether PCSK9 could play a role in NPC1 disease progression. We addressed this question genetically, by characterizing NPC1 disease in the presence or absence of PCSK9. Analysis of double mutant Pcsk9-/-/Npc1-/- mice by disease severity scoring, motor assessments, lifespan, and cerebellar Purkinje cell staining, showed no obvious difference in NPC1 disease progression with that of Npc1-/- mice. This suggests that PCSK9 does not play an apparent role in NPC1 disease progression.
| S-EPMC7178166 | biostudies-literature
Project description:Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a secreted protein that promotes degradation of cell surface LDL receptors (LDLRs) in selected cell types. Here we used genetic and pharmacological inhibitors to define the pathways involved in PCSK9-mediated LDLR degradation. Inactivating mutations in autosomal recessive hypercholesterolemia (ARH), an endocytic adaptor, blocked PCSK9-mediated LDLR degradation in lymphocytes but not in fibroblasts. Thus, ARH is not specifically required for PCSK9-mediated LDLR degradation. Knockdown of clathrin heavy chain with siRNAs prevented LDLR degradation. In contrast, prevention of ubiquitination of the LDLR cytoplasmic tail, inhibition of proteasomal activity, or disruption of proteins required for lysosomal targeting via macroautophagy (autophagy related 5 and 7) or the endosomal sorting complex required for trafficking (ESCRT) pathway (hepatocyte growth factor-regulated Tyr-kinase substrate and tumor suppressor gene 101) failed to block PCSK9-mediated LDLR degradation. These findings are consistent with a model in which the LDLR-PCSK9 complex is internalized via clathrin-mediated endocytosis and then routed to lysosomes via a mechanism that does not require ubiquitination and is distinct from the autophagy and proteosomal degradation pathways. Finally, the PCSK9-LDLR complex appears not to be transported by the canonical ESCRT pathway.
| S-EPMC3413232 | biostudies-literature
Project description:Proprotein convertase subtilisin/kexin type 9 (PCSK9) regulates expression of low-density lipoprotein (LDL) receptors via receptor internalization and subsequent lysosomal degradation. Thus, an anti-PCSK9 antibody is well known as an anti-hyperlipidemia drug. Here, we aimed to develop vaccine for a long-term treatment of dyslipidemia targeted to PCSK9. In This study, we designed a peptide vaccine for mouse PCSK-9, which consisted of short peptides conjugated to keyhole limpet hemocyanin (KLH) as a carrier protein. Vaccines were administered to male apolipoprotein E (ApoE) deficient mice with adjuvants and significantly elicited an antibody response against PCSK9. The PCSK9 vaccines were administered to mice three times in 2-week intervals, and antibody titers and lipoprotein levels were evaluated up to 24 weeks after the first immunization to determine the therapeutic effect. Anti-PCSK9 antibody titers reached peak levels 6 weeks after the first immunization, and theses titers were maintained for up to 24 weeks. Decreased plasma levels of total cholesterol, very low-density lipoprotein (VLDL), and chylomicron (CM) were maintained for up to 24 weeks. Immunized mice exhibited a significant increase in cell-surface LDL receptor expression. Stimulation with KLH, but not PCSK9, induced the production of INF-gamma and interleukin-4 (IL-4), as determined with ELISPOT assays, thus indicating that PCSK9 vaccine did not elicit T-cell activation in our vaccine system. The present anti-PCSK9 vaccine induced long-lasting anti-PCSK9 antibody production and improved lipoprotein profiles. Thus, anti-PCSK9 vaccine could become a new option for the treatment of dyslipidemia as a long-acting therapy in future.
| S-EPMC5811007 | biostudies-literature