Proprotein Convertase Subtilisin / Kexin Type-9 (PCSK9) has emerged as a major regulator of plasma cholesterol levels. PCSK9 is secreted mainly from the liver and circulates as a plasma protein. PCSK9 binds cell surface low-density lipoprotein (LDL) receptors and mediates their degradation upon endocytosis in the liver. This decreases the liver’s ability to clear LDL-cholesterol from the blood. PCSK9 is also capable of binding LDL particles themselves; this interaction inhibits the ability of PCSK9 to bind and mediate LDLR degradation in cultured hepatic cells, but its effect on PCSK9 function in vivo remains unknown. A disordered N-terminal region of the PCSK9 prodomain is necessary for binding to isolated LDL particles in vitro. This N-terminal region is also autoinhibitory to PCSK9-LDL receptor binding. We hypothesized that the N-terminal of the PCSK9 prodomain plays a role in an allosteric mechanism that regulates PCSK9 function. Through mutagenesis studies, we found that both a conserved stretch of acidic residues and an adjacent conserved stretch of hydrophobic residues are crucial for the PCSK9-LDL interaction; the hydrophobicity of the residue at position 38 (Tyr) within the conserved acidic stretch was also found to be important for this. Helical wheel modeling of the prodomain N-terminal sequence revealed the potential for a lipid-ordered amphipathic helix to form, which may aid PCSK9 docking onto LDL. Replacing residues A44 and L41 with helix-disrupting proline residues abolished LDL binding. Co-pelleting ultracentrifugation assays also show that wild-type PCSK9 is capable of associating with liposomes, while the A44P mutation disrupts this lipid association. The A44P-PCSK9 mutation, showing an 80-90% decrease in LDL association but with LDL receptor binding and degrading functions intact, may serve as an important tool in future studies investigating the PCSK9-LDL interaction in vivo. Elucidation of the mechanism by which LDL-binding naturally inhibits PCSK9 activity may also help to develop new anti-PCSK9 therapeutics in the future.

Hypercholesterolemia is one of the most prevalent, yet underdiagnosed diseases faced by the medical community today. Its prevalence can largely be attributed to diet, lack of exercise, and lifestyle choices such as smoking or drinking, but there is also a genetic component. Familial Hypercholesterolemia is the genetic disorder in which a person is unable to properly eliminate levels of low-density lipoprotein, mostly due to an ineffective receptor in the liver. Hypercholesterolemia has been positively correlated with the prevalence of cardiovascular disease, and patients with the severe homozygous familial hypercholesterolemia typically have abbreviated lifespans. In these situations, and also those less acutely dire, it’s necessary to rely on medication to help maintain one’s cholesterol levels to within low risk ranges. High does statin therapy has been shown to be the most effective therapy for maintaining LDL cholesterol. It has become the standard regardless of the cause of hypercholesterolemia because of its few side effects, its high tolerability, its ease of administration, its safety, and most of all because of its immense efficacy. This has not, however, prevented the exploration into other types of cholesterol therapies that may work in concurrence with statins. Drug classes such as PCSK9 inhibitors, ApoB inhibitors, MTP inhibitors, and thyromimetics have all been explored with varying success. Each of these potential therapies has a separate mechanism of action, allowing for modulation in conjunction with statins. PCSK9 inhibitors and ApoB inhibitors appear to provide the most upside by virtue of LDL lowering capabilities, followed by a drug known as ezetimibe that reduces dietary cholesterol uptake in the gut. MTP inhibitors have been shown to be effective therapies for homozygous familial hypercholesterolemia specifically due to their function of lowering LDL particle creation rather than LDL receptor number or function as statins and PCSK9 inhibitors do. Thyromimetics have yet to yield an effective therapy for cholesterol treatment, but the hope remains alive that this could come to fruition in the future.

L’intestin est un acteur majeur du métabolisme du cholestérol de part son rôle dans dans l’absorption, la sécrétion des lipoprotéines et l’efflux transintestinal de cholestérol (TICE). De plus, c’est le second organe majeur, après le foie, à exprimer la Proproteine Convertase Subtilisine Kexine de type 9 (PCSK9), un inhibiteur naturel du récepteur aux LDL. Notre analyse des mécanismes moléculaires impliqués dans l’ hypocholestérolémie induite par les chirurgies bariatriques montre que la sleeve gastrectomie induit une hypocholestérolémie transitoire et modérée lié aux modifications de prise alimentaire. En revanche, le by-pass Roux en Y (RYGB) réduit fortement la cholestérolémie, stimule significativement son élimination fécale en induisant le TICE et en réduisant l’absorption intestinale de cholestérol. La seconde partie de ma thèse visait à répondre à une controverse autour de la faculté de l’intestin à sécréter PCSK9. In vivo (souris) et ex vivo (souris et homme), il ne semble pas que les cellules intestinales matures sécrètent PCSK9. En revanche, nous confirmons que la lignée humaine Caco2 est capable de sécréter PCSK9 mais que cette sécrétion est abolie lorsque les cellules deviennent matures. Les mécanismes responsables de cette perte de sécrétion restent mal définies mais sont dues au moins à deux paramètres: 1) une réduction du contenu intracellulaire induite par un catabolisme lysosomal accru; 2) une modification posttraductionelle de PCSK9 (glycosilation) altérant les voies de sécrétion post-Golgiennes. Les cellules Caco2 constituent un outil précieux pour disséquer les mécanismes et partenaires protéiques nécessaires à la sécrétion de PCSK9. Leurs identifications pourraient permettre de développer de nouveaux inhibiteurs pour réduire la sécrétion de PCSK9, réduire l’hypercholestérolémie et lutter plus efficacement contre les maladies cardiovasculaires. / The intestine is a major actor of cholesterol metabolism from its role in absorption, secretion of lipoproteins and transintestinal cholesterol efflux (TICE). In addition, it is the second major organ, after the liver, to express the Proproteine Convertase Subtilisin Kexin type 9 (PCSK9), the natural inhibitor of the LDL receptor. Our analysis of molecular mechanism involved in hypocholesterolemia induced by bariatric surgeries shows that the gastrectomy sleeve induces a transient and moderate hypocholesterolemia linked to the modification of the food intake. In contrast, the Roux-Y by-pass (RYGB) strongly reduces cholesterol, significantly stimulates its fecal elimination by inducing TICE and decreasing intestinal absorption of cholesterol. The second part of my thesis consisted to elucidate the controversy around the faculty of the intestine to secrete PCSK9. In vivo (mice) and ex vivo (mice and human), it seems that mature enterocytes can’t secrete PCSK9. On the other hand, we confirm that the Caco2, an human intestinal cell line, is capable of secreting PCSK9, but this secretion is abolished when the cells become mature. Mechanisms responsible for this loss of secretion remain poorly defined and are, at least, due to: 1) a reduction in the intracellular content induced by increased lysosomal catabolism; 2) a post-translational modification of PCSK9 (glycosilation) altering post-Golgi secretion pathways. Caco2 cells are a powerfull tool for identify the mechanisms and partners required for the secretion of PCSK9. Their identifiers allow the development of new inhibitors to reduce the secretion of PCSK9, reduce hypercholesterolemia and fight more effectively against cardiovascular diseases.

The proprotein convertase subtilisin/kexin type 9 (PCSK9) was first characterized in 2003 by Seidah and colleagues and marked the beginning of what is now considered by many as the greatest advancement in the field of cardiovascular disease (CVD) research since the discovery of the LDLR nearly half of a century ago. Since its discovery, PCSK9 was shown to enhance the degradation of cell-surface low-density lipoprotein (LDL) receptor (LDLR) and gain-of-function (GOF) mutations were shown to correlate with CVD risk. In contrast, patients carrying loss-of-function (LOF) mutations in PCSK9 highlighted a novel therapeutic approach for LDL lowering as they exhibit a life-long state of hypocholesterolemia and reduced CVD risk. A decade after the cloning of the PCSK9 gene, pharmaceutical companies have now developed a variety of PCSK9 inhibitors, ranging from monoclonal antibodies (mAbs) to small interfering RNA (siRNA) and vaccines, which have been shown to markedly reduce LDL cholesterol levels in pre-clinical models, as well as in patients at high risk of CVD. Despite these advances, there remained several unanswered questions regarding the mechanisms by which PCSK9 expression and secretion is regulated in the liver; the tissue from which the circulating pool of PCSK9 almost exclusively originates. The thought that further development of our understanding of PCSK9 biology may lead to the discovery of a signaling cascade that could be targeted by small molecules, the only class of inhibitor that has not yet been developed, has now merited additional research attention. The focal point of my doctoral studies represents the axis between a cellular process known as endoplasmic reticulum (ER) stress and PCSK9 expression/biosynthesis. ER stress is a deleterious cellular process that is known to occur in secretory cell types, such as liver hepatocytes, and is a well-established causative driver of an array of human diseases ranging from CVD to neurodegenerative diseases. ER stress is prevalent in the livers of patients with metabolic disease and is also known to activate the transcription factor capable of regulating PCSK9 levels, the sterol regulatory element-binding protein 2 (SREBP2). Based on this information, the first aim during the course of my PhD studies was to determine whether ER stress affected the expression and secretory status of PCSK9. In the past several years, I demonstrated that ER stress caused by ER Ca2+ depletion led to a marked increase in PCSK9 protein expression, but blocked its secretion as a result of its retention in the ER. Such a result was also associated with heightened hepatic LDLR expression and reduced LDL cholesterol levels in mice. Additional studies also characterized a variety of agents, including caffeine, as potent inhibitors of PCSK9 expression via increasing ER Ca2+ levels, which antagonized SREBP2 activity. As our initial studies revealed ER PCSK9 retention as a viable strategy for PCSK9 inhibition and LDL lowering, follow-up studies were also carried out to determine the outcome of such a strategy on liver function and injury. Given that heritable mutations in proteins that transit the ER can accumulate in this compartment and cause ER storage disease (ERSD), it was critical to further evaluate whether ER PCSK9 retention would lead to a similar outcome. In a series of experiments with rather surprising outcomes, we observed that the retention of the LOF Q152H PCSK9 mutant in the ER failed to cause ER stress; even in mice overexpressing the protein. Interestingly, tissue culture and mouse models demonstrated that the retention of PCSK9 in this cellular compartment increased the cellular abundance of ER stress response chaperones, such as the glucose-regulated proteins of 78- and 94-kDa (GRP78 and GRP94, respectively), but did not activate transducers of the ER stress signaling cascade. Strikingly, mice expressing the ER-retained PCSK9 Q152H mutant were protected against ER stress, suggesting a novel co-chaperone-like role of intracellular PCSK9. Collectively, the ER environment including secondary messengers like Ca2+ as well as its chaperones, plays a critical regulatory role on PCSK9 expression and secretion. Agents that increase ER Ca2+ levels can be utilized to block PCSK9 expression at the mRNA level to increase hepatic LDL clearance, and ER PCSK9 retention may also represent a safe avenue with a similar LDL lowering outcome. Beyond LDL lowering, hepatic ER PCSK9 retention may also serve as a novel strategy to enhance ER function and protect against ER stress-driven diseases of the liver. / Thesis / Doctor of Philosophy (Medical Science)

A Hipercolesterolemia Familial (HF) é uma doença genética do metabolismo das lipoproteínas, caracterizada pelo aumento do colesterol plasmático, transportado principalmente pela lipoproteína de baixa densidade (LDL). A HF é causada principalmente por mutações nos genes LDLR, APOB e PCSK9. As mutações conhecidas na PCSK9 podem levar ao aumento ou diminuição da função proteolítica da proteína, as quais são associadas ao aumento ou diminuição da LDL-c plasmática, respectivamente. Com o projeto genoma humano surgiram novos métodos de sequenciamento, o que resultou em um grande número de novas variantes genéticas relacionadas à HF. Entretanto, os mecanismos pelos quais essas variantes influenciam na concentração do colesterol e sua interferência na resposta terapêutica não estão totalmente elucidados. O objetivo do presente trabalho foi avaliar in vitro o efeito de variantes na região codificadora e reguladora do gene PCSK9 identificadas em pacientes HF utilizando sequenciamento de nova geração. Para a caracterização funcional das variantes na região codificadora da PCSK9, primeiramente foi avaliado o impacto dessas variantes na interação PCSK9-LDLR via Docking molecular. Células HEK293FT foram transfectadas com as diferentes construções da PCSK9, e posteriormente, foram utilizadas em ensaios para avaliar a atividade do LDLR e a internalização de LDL por citometria de fluxo. Para as variantes na região reguladora da PCSK9, foi realizado uma predição in silico do possível efeito de variantes na região 3UTR na ligação de miRNAs. A avalição da interação entre os miRNAs preditos, e a região 3UTR da PCSK9, e o possível impacto nessa interação na presença de variantes na região 3UTR, foi realizada em células HEK293FT transfectadas com um plasmídeo contendo a 3UTR da PCSK9 e um gene repórter da Gaussia luciferase, juntamente com um plasmídeo de expressão contendo os miRNAs de interesse. Foi também estudado o efeito dos miRNAs preditos sobre a expressão, RNAm e proteína, da PCSK9 via RT-qPCR e Western blot, em células HepG2. Foram identificadas 9 variantes na região codificadora da PCSK9, e duas, E32K e R469W, foram selecionadas para os ensaios posteriores. Para a R469W foi observada uma possível alteração conformacional a qual poderia aumentar a afinidade da PCSK9 pelo LDLR. Para a E32K, uma possível associação com HF foi observada em uma família brasileira com ascendência japonesa. As variantes E32K e R469W apresentaram uma redução na atividade do LDLR de 5 e 11%, respectivamente em comparação a PCSK9-WT. Entretanto, não foram observadas reduções estaticamente significativas na atividade do LDLR e na internalização da LDL em células transfectadas com ambas as variantes. Dez variantes foram encontradas na região 3UTR da PCSK9, entre elas três foram selecionadas por impactar a ligação de quatro miRNAs. Nossos dados demonstraram uma redução significativa na expressão da PCSK9 em células HepG2 transfectadas com os miR-4721 e miR-564 (p=0,036 e p=0,010, respectivamente). Porém, não foi observada diferenças na expressão da luciferase em células transfectadas com esses miRNAs, não sendo possível validar a interação miRNA-RNAm. As variantes no gene PCSK9 identificadas no nosso estudo podem não explicar individualmente o fenótipo HF, mas podem contribuir para a severidade da doença juntamente com outras variantes em outros genes. / Familial Hypercholesterolemia (FH) is a genetic disorder of lipoprotein metabolism, characterized by elevated plasma cholesterol levels, mostly carried by low-density lipoprotein (LDL). FH is mainly caused by mutations in three genes, LDLR, APOB, and PCSK9. Gain-of-function mutations in PCSK9 reduce LDL receptor levels, resulting in high levels of LDL cholesterol in the plasma. Loss-of-function mutations lead to higher levels of the LDL receptor, resulting in lower LDL cholesterol levels. The Human Genome Project led to a faster technological development related to sequencing methods, which allowed identifying many novel variants associated with FH. However, the mechanisms by which these variants influence cholesterol levels and their interference in therapeutic response are not fully understood. The aim of the present study was to perform an in vitro characterization of the effect of PCSK9 variants identified in FH patients using Next-Generation Sequencing. For the functional characterization of variants in the coding region of PCSK9, the impact of these variants on PCSK9-LDLR interaction was evaluated by molecular docking. HEK293FT cells were transiently transfected with different PCSK9 constructs, and the amount of cell surface LDLR and LDL internalization were determined by flow cytometry. For the variants in PCSK9 3UTR region, an in silico prediction of PCSK9 3UTR variants in miRNA seed regions and target sites was performed. To determine whether the predicted miRNAs directly interact with PCSK9 3UTR region, HEK293FT cells were co-transfected with a vector containing a PCSK9 3\'UTR region and a Gaussia luciferase reporter gene, together with an expression plasmid containing the miRNAs of interest. The effect of the predicted miRNAs on the expression of PCSK9 was evaluated using RT-qPCR and Western blot in HepG2 cells transiently transfected with miRNA mimics. Nine missense variants were identified in PCSK9 gene. E32K e R469W were chosen for further analysis. For R469W, a possible conformational change was observed that could increase the affinity of PCSK9 for LDLR, when compared to the wild-type. For E32K, a possible association with FH in a Brazilian family with Japanese ancestry was observed. E32K and R469W had a 5% and 11% decreased level of cell surface LDLR, respectively, as compared with WT-PCSK9. However, no significant reduction in the number of cell surface LDLR and LDL internalization was observed in transfected cells for both variants. Ten variants were found in PCSK9 3\'UTR region, of which three were selected for affecting the binding of four miRNAs. Our data demonstrated a significant downregulation of PCSK9 in cells transfected with miR-4721 and miR-564 miRNA mimics, compared to cells transfected with a scramble control (p=0,036 and p=0,010, respectively). However, no differences in luciferase expression were observed in cells transfected with these miRNAs, therefore, it was not possible to experimentally validate miRNA-mRNA interaction. PCSK9 variants found in our study may not fully explain FH phenotype but may contribute to the severity of the disease together with other variants in other genes.

A frequência de Hipercolesterolemia Familial (HF) ainda é desconhecida no Brasil, principalmente pela ausência de estudos com caracterização genotípica associada à fenotípica. Os dados epidemiológicos existentes se baseiam apenas no fenótipos e carecem do diagnóstico molecular confirmatório. O objetivo do presente estudo foi identificar as principais causas genéticas da HF em pacientes diagnosticados fenotipicamente através de um painel exômico com 61 genes a fim de contribuir para um sistema de confirmação do diagnostico molecular em uma amostra da população brasileira. Para isso foram incluídos 141 pacientes, não aparentados, portadores de HF atendidos pelo setor de dislipidemias do Instituto Dante Pazzanese de Cardiologia, Laboratório de Analises Clinicas da Faculdade de Ciências Farmacêuticas da Universidade Federal do Rio Grande do Norte e do Programa Hipercol Brasil do Instituto do Coração. As amostras de sangue periférico foram obtidas para determinações fenotípicas laboratoriais e extração de DNA genômico. A biblioteca de DNA foi construída utilizando o kit Nextera® Rapid Capture Enrichment Custom enriquecendo os éxons de 61 genes que direta ou indiretamente estão relacionados com metabolismo do colesterol. O ultrassequenciamento foi realizado utilizando kit MiSeq Reagent (300 a 500 ciclos) na plataforma MiSeq (Illumina). Os resultados de sequenciamento foram inicialmente alinhados a uma sequência referência e analisados para eliminação de falsos positivos, segundo os parâmetros de qualidade, tais como: cobertura mínima de 30x, frequência do alelo alterado maior que 20% e diferença da distribuição das leituras entre as sequências nucleotídicas menor que 15%. Foram identificadas 472 diferentes variantes em 56 dos genes presentes no painel, sendo 45 consideradas como não descritas. Nos genes APOA1, APOA2, LIPC, RBP4 e TIMP1 não foram observadas variantes dentro dos critérios estabelecidos. Das variantes observadas 25 identificadas em 30 (21,2%) pacientes já tinha sido publicadas em relação à HF nos três principais genes (LDLR, APOB e PCSK9), confirmando o diagnóstico. Foi caracterizado genotipicamente outras dislipidemias primárias em 7 pacientes, sem diagnóstico molecular de HF, através de variantes identificadas no ultrassequenciamento em outros genes. Dos 104 pacientes que não possuíam nenhuma variante já previamente caracterizada, 69 possuíam variantes relacionados com o metabolismo do colesterol. As variantes sem patogenicidade conhecida foram avaliadas através de ferramentas de predição in silico e 22 delas possuíam características sugestivas de patogenicidade em pelo menos 4 das ferramentas utilizadas, duas delas também mostraram alterar a estrutura da proteína segundo análises de docking molecular. Foram identificadas também 223 variantes em região não transcritas (UTR). Quando realizada as análises estatística de todas as variantes identificadas, observamos associação de 13 variantes com concentrações mais elevadas de colesterol da LDL, 5 com concentrações mais elevadas de apolipoproteina B-100, 5 com concentrações mais elevadas de colesterol total, 6 com presença de arco córneo, 2 com manifestação de xantelasmas, 2 com ausência de xantomas e 3 com a presença de doença arterial coronariana. Dessas 6 variantes já haviam sido previamente descritas com HF ou algum outro fenótipo associado e 2 não tinham citação na literatura pesquisada, mas possuíam característica patogênica para a proteína segundo as ferramentas de predição in silico. Este estudo permitiu a identificação das causas genéticas da HF em pacientes brasileiros diagnosticados fenotipicamente, mostrando que a técnica escolhida permitiu caracterizar 21,2% dos pacientes. Além disso, foi possível identificar outras dislipidemias primárias e caracterizar algumas variantes que, apesar de necessitarem serem validadas, indicam uma possível associação com a HF, aumentando o esclarecimento do fenótipo com o genótipo para 74,5%. Este estudo também possibilitou a identificação de novas variantes que devem ser avaliadas para confirmar associação com a doença e utilizar para o diagnóstico propondo um novo painel poligênico. / The frequency of Familial Hypercholesterolemia (FH) is still unknown in Brazil, mainly due to the absence of studies with genotypic characterization associated with phenotype. Existing epidemiological data are based only on the phenotypes and lack the confirmatory molecular diagnosis. The aim of the present study was to identify main genetic causes of FH in patients diagnosed phenotypically through an exomic panel with 61 genes in order to contribute to a system of confirmation molecular diagnosis in a sample of the Brazilian population. To this end, 141 non-related patients with FH treated by the dyslipidemia sector of the Institute Dante Pazzanese of Cardiology, Clinical Analysis Laboratory of the Faculty of Pharmaceutical Sciences of the University Federal of Rio Grande do Norte and the Hipercol Brazil Program of the Heart Institute. Peripheral blood samples were obtained for laboratory phenotypic determinations and extraction of genomic DNA. The DNA library was constructed using the Nextera® Rapid Capture Enrichment Custom kit, enriching with éxons of 61 genes that are directly or indirectly related to cholesterol metabolism. Ultrasequencing was performed using MiSeq Reagent kit (300 to 500 cycles) on the MiSeq platform (Illumina). The sequencing results were initially aligned to a reference sequence and analyzed for false positive elimination according to quality parameters such as: minimum coverage of 30x, altered allele frequency greater than 20%, and difference in the distribution of reads between sequences nucleotides less than 15%. 472 different variants were identified in 56 of the genes present in the panel, of which 45 were considered not described. In the APOA1, APOA2, LIPC, RBP4 and TIMP1 genes no variants were observed within the established criteria. In 25 of the variants observed presents in 30 (21.2%) patients had already been published in relation to FH in the three main genes (LDLR, APOB and PCSK9), confirming the diagnosis. Other primary dyslipidemias were caracterized genotypically in 7 patients, without molecular diagnosis of HF, through variants identified in ultrasequencing in other genes. Of the 104 patients who did not have any previously characterized variant, 69 had variants related to cholesterol metabolism. The variants without known pathogenicity were evaluated using in silico prediction tools and 22 of them had characteristics suggestive of pathogenicity at least 4 of the tools used, two of them also showed to alter the structure of the protein according to molecular docking analyzes. Were also identified 223 non-transcribed region (UTR) variants. Statistical analysis of all the variants identified showed association of 13 variants with higher concentrations of LDL cholesterol, 5 with higher concentrations of apolipoprotein B-100, 5 with higher concentrations of total cholesterol, 6 with presence of an arc corneal, 2 with manifestation of xanthelasms, 2 with absence of xanthomas and 3 with the presence of coronary artery disease. Of these 6 variants had previously been described with HF or some other associated phenotype and 2 had no citation in the researched literature, but had a pathogenic characteristic for the protein according to in silico prediction tools. This study allowed the identification of the genetic causes of FH in Brazilian patients diagnosed phenotypically, showing that the technique chosen allowed to characterize 21.2% of the patients. In addition, it was possible to identify other primary dyslipidemias and to characterize some variants that, although they need to be validated, indicate a possible association with HF, increasing the clarification of the phenotype with the genotype to 74.5%. This study also allowed the identification of new variants that should be evaluated to confirm association with the disease and to use for the diagnosis proposing a new polygenic panel.

Atherosclerosis is the underlying cause for many serious cardiovascular diseases which causes over 50 % of all deaths in Sweden. Atherosclerotic plaque builds up in the vessel walls over decades that will eventually lead to a complete block of an artery or cause thrombosis when the plaque ruptures, this leads to myocardial infarction and stroke. A major contributing factor to the buildup of plaque is cholesterol, especially low density lipoprotein, LDL. LDL can oxidize and start an inflammation process and together with cells from the immune system form the basis for a plaque. Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a protein which main function is to regulate the amount of LDL-receptors available by promoting their degradation. PCSK9 causes degradation of the receptors with the effect that more LDL is left in the blood stream. Evolocumab is a monoclonal antibody with PCSK9 as the target, with PCSK9 neutralised less LDL will be left in the blood stream which will help prevent atherosclerosis. This is a complex and expensive way of treating atherosclerosis, the primary treatment is statins and secondarily cholesterol absorbtion inhibitors, bile acid sequestrants and fibrates. The purpose of this study was to examine evolocumabs effect on cardiovascular events in high risk patients and for which patient groups it is cost-efficient. The method used was searching the medical database PubMed with the keywords “evolocumab” and “evolocumab cost-effectiveness”. 5 articles was analysed and they showed that evolocumab lowered LDL-cholesterol with 55-60 % and significantly improved the lipid profile of patients. The hazard risk was lowered by 20-25 % for serious cardiovascular events and a 10 % lower rate of death was assessed after 5 years of treatment. Since no large studies have followed up on patients for over 5 years and measured cardiovascular events and deaths it is hard to know for sure how efficient evolocumab is at preventing death. The price of evolocumab is 50 000 SEK for one year of treatment and to assess which patients should be treated proved difficult due to the facts that the Swedish national regions have a side deal with the drug manufacturer Amgen in which they get compensation if evolocumab would prove to not be cost-efficient enough and there is no fixed acceptable price per quality adjusted life year (QALY) in Sweden. / Ateroskleros är grund till många allvarliga hjärt- och kärlsjukdomar och ligger bakom mer än hälften av alla dödsfall i Sverige. Sjukdomen innebär att plack byggs upp i kärlväggarna under flera decennier och till slut täpper igen ett kärl eller brister och en blodpropp bildas vilket leder till hjärtinfarkt och stroke. En bidragande faktor till bildningen av aterosklerotiska plack är kolesterol främst i form av lågdensitetlipoprotein (LDL), oxiderat LDL bidrar till att en inflammationsprocess startar i kärlet. Proprotein konvertas subtilisin/kexin typ 9 (PCSK9) är ett protein vars uppgift är att reglera antalet LDL-receptorer genom att binda in till receptorerna och ”märka” ut dem för nedbrytning. Evolokumab är en antikropp mot PCSK9 vars effekt ökar antalet LDL-receptorer vilket i sin tur minskar mängden LDL i blodet. Evolokumab är ett nytt och dyrt läkemedel, ateroskleros behandlas istället främst med statiner men också med kolesterolabsoptionshämmare, resiner och fibrater. Syftet med arbetet var att undersöka evolokumabs effekt att minska risk för hjärt- och kärlsjukdomar samt för vilka patientgrupper det är kostnadseffektivt. Metoden som användes var att söka artiklar på PubMed med sökorden ”Evolocumab” och ”Evolocumab cost effectiveness”. Fem artiklar undersöktes och de visade att evolokumab sänker LDL-kolesterolet i blodet med 55-60 % och även andra lipidvärden förbättras betydligt. Riskminskningen att drabbas av hjärt- och kärlsjukdomar bedömdes vara 20-25 % och riskminskningen att dö till följd av dessa sjukdomar uppskattades till 10 % efter 5 års behandling för patienter med hög risk att drabbas av dessa sjukdomar. Standardbehandling med evolokumab ger en kostnad på 50 000 kr per år för läkemedlet och angående vilka patienter som bör få Evolokumab är det svårt att göra en gränsdragning då det i Sverige finns en sidoöverenskommelse som innebär att tillverkaren kompenserar landstingen om behandlingen inte är kostnadseffektiv samt att i Sverige finns inget fast värde för ett kvalitetsjusterat levnadsår (QALY).

The discovery that proprotein convertase subtilisin/kexin type 9 (PCSK9) mediates degradation of low-density lipoprotein receptors (LDLR) indicates a critical role in LDL metabolism. PCSK9 is a secreted protein that binds to the epidermal growth factor-like (EGF)-A domain of LDLR and directs the receptor for degradation in lysosomes by an unknown mechanism. A gain-of-function mutation, D374Y, increases binding to LDLR EGF-A >10-fold and is associated with a severe form of hypercholesterolemia in humans. Similar to previous studies, data obtained in my project has established that PCSK9 was capable of promoting robust LDLR degradation in liver-derived cell lines; however, minimal effects on LDLR levels were detected in several lines of fibroblast cells despite normal LDLR-dependent cellular uptake of PCSK9. Importantly, a PCSK9 degradation assay showed that 125I-labeled wild-type PCSK9 was internalized and degraded equally in both hepatic and fibroblast cells, indicating dissociation of wild-type PCSK9 from recycling LDLRs in fibroblasts. Moreover, PCSK9 recycling assays confirmed that no recycling of wild-type PCSK9 to the cell surface could be detected in fibroblast cells. In contrast, more than 60% of internalized PCSK9-D374Y recycled to the cell surface in these cells, and thus had reduced ability to direct the LDLR for lysosomal degradation despite persistent binding. Co-localization studies indicated that PCSK9-D374Y trafficked to both lysosomes and recycling compartments in fibroblast cells, whereas wild-type PCSK9 exclusively trafficked to lysosomes. We conclude that two factors diminish PCSK9 activity in fibroblast cells: i) an increased dissociation from the LDLR in early endosomal compartments, and ii) a decreased ability of bound PCSK9 to direct the LDLR to lysosomes for degradation. Finally, an LDLR variant that binds to PCSK9 in a Ca2+-independent manner could partially restore wild-type PCSK9 activity, but not PCSK9-D374Y activity, in fibroblast cells.

The discovery that proprotein convertase subtilisin/kexin type 9 (PCSK9) mediates degradation of low-density lipoprotein receptors (LDLR) indicates a critical role in LDL metabolism. PCSK9 is a secreted protein that binds to the epidermal growth factor-like (EGF)-A domain of LDLR and directs the receptor for degradation in lysosomes by an unknown mechanism. A gain-of-function mutation, D374Y, increases binding to LDLR EGF-A >10-fold and is associated with a severe form of hypercholesterolemia in humans. Similar to previous studies, data obtained in my project has established that PCSK9 was capable of promoting robust LDLR degradation in liver-derived cell lines; however, minimal effects on LDLR levels were detected in several lines of fibroblast cells despite normal LDLR-dependent cellular uptake of PCSK9. Importantly, a PCSK9 degradation assay showed that 125I-labeled wild-type PCSK9 was internalized and degraded equally in both hepatic and fibroblast cells, indicating dissociation of wild-type PCSK9 from recycling LDLRs in fibroblasts. Moreover, PCSK9 recycling assays confirmed that no recycling of wild-type PCSK9 to the cell surface could be detected in fibroblast cells. In contrast, more than 60% of internalized PCSK9-D374Y recycled to the cell surface in these cells, and thus had reduced ability to direct the LDLR for lysosomal degradation despite persistent binding. Co-localization studies indicated that PCSK9-D374Y trafficked to both lysosomes and recycling compartments in fibroblast cells, whereas wild-type PCSK9 exclusively trafficked to lysosomes. We conclude that two factors diminish PCSK9 activity in fibroblast cells: i) an increased dissociation from the LDLR in early endosomal compartments, and ii) a decreased ability of bound PCSK9 to direct the LDLR to lysosomes for degradation. Finally, an LDLR variant that binds to PCSK9 in a Ca2+-independent manner could partially restore wild-type PCSK9 activity, but not PCSK9-D374Y activity, in fibroblast cells.

Background Elevated concentrations of low-density lipoprotein cholesterol (LDL-c) are a major risk factor for the development of coronary artery disease (CAD) because of their role in the progression of atherosclerosis. The black South African population is known to have had historically low LDL-c and in the past there was almost no CAD in the population. However, as this population moves through the nutrition transition, LDL-c levels are increasing. LDL-c levels are regulated by the LDL receptors, which is the major protein involved with transporting cholesterol across cell membranes in humans. Proprotein convertase subtilisinlike/kexin type 9 (PCSK9) is another protein involved with the regulation of LDL-c through its role in assisting with the degradation of the LDL receptor. Variants in both genes can cause elevated or lowered LDL-c levels. Very little information is available on the frequency or presence of variants in the low-density lipoprotein receptor (LDLR) and PCSK9 gene in the black South African population and on how these variants associate with LDL-c. The main aim of the study was thus to determine novel and existing genetic variants in these two genes and to describe the manner in which they associate with plasma LDL-c levels in a black South African population undergoing an epidemiological transition. Methods The 2005 baseline data from the Prospective Urban and Rural (PURE) study population were used in this study. The study population consisted of apparently healthy black volunteers form the North West province of South Africa, aged 35 to 60 years. Thirty individuals were randomly chosen from the 1860 volunteers to determine the presence of known and novel variants in these genes by automated bidirectional sequencing. The promoter region, exons and flanking regions were sequenced and variants were identified utilising CLC DNA Workbench. Deoxyribonucleic acid (DNA) samples for 1500 individuals of the PURE study population were genotyped by means of a Golden Gate Genotyping Assay. Analyses of covariance (ANCOVA) were used to test for associations between the different genotypes in both the LDLR and PCSK9 genes and LDL-c levels. Haplotypes were generated by using the confidence intervals on the software programme, HaploView. A genetic risk score (GRS) was determined by including variants which associated significantly with LDL-c. The GRS, the haplotypes and the variants that associated significantly with LDL-c were used in separate linear regression models with variants which correlated with LDL-c to determine how all these variables contribute to the differences in LDL-c levels. Results and discussion Novel and known variants were identified in both the genes and in total 52 variants were genotyped. Rare variants such as rs17249141 and rs28362286 were detected in the study population and are associated with low levels of LDL-c. The variants identified in the LDLR gene were situated largely in regulatory regions such as the promoter, intron and 3‟untranslated regions. Haplotypes in the LDLR gene with the highest frequency associated with lower LDL-c levels, which could contribute to the study population‟s low mean LDL-c level. Haplotypes identified in the PCSK9 gene had a weaker association with LDL-c levels. The minor allele frequencies of many of the variants differed from those of the European population and therefore the importance of population-specific research cannot be sufficiently emphasised. The GRS, haplotypes and variants used in the regression models to determine whether they contributed to predicting the variance in LDL-c in the study population made a small contribution to explaining this. BMI best explained the variance in LDL-c levels. Older women with a body mass index (BMI)>25kg/m2 were identified as being at greater risk of developing elevated LDL-c levels than the rest of the study population. Heterozygote carriers of variant, rs28362286, had 0.787 mmol/L lower LDL-c than carriers of the wild type and this is associated with a reduced risk of developing CAD. Conclusion and recommendation When considering the results mentioned above, adding genetic analysis to explaining the variance in LDL-c levels seems to have its limitations, but the study included only two of many genes that play a role in the metabolism and regulation of LDL-c levels. Incorporating more genes and more variants into analyses and prediction models will add greater value to defining LDL-c levels. Rarer variants with a large impact on protein function, such as rs28362286, have a greater effect on LDL-c levels and could predict the variance better than the common variants. Risk factors such as BMI can also still be trusted to indicate which individuals or groups are at risk of developing elevated LDL-c levels. Health advice should be given to appropriate target groups such as older women with a BMI >25kg/m2 in order to prevent CAD from becoming a burden in this population. / PhD (Dietetics), North-West University, Potchefstroom Campus, 2014