Leveraging miRNA-Seq data and the 1000 Genomes imputed genotypes, we identified rs174561-C as a strong miRQTL for circulating miRNA-1908-5p (P=4.8x10-31) which has an inverse relationship with circulating LDL-C, fasting glucose and A1c. Here I investigated the molecular mechanism(s) linking miR1908-5p to cholesterol metabolism. First, by overexpression experiments in HuH-7 cells demonstrate that the presence of the C allele, associated with lower LDL-C levels, significantly increases miR-1908-5p by 2.15-fold relative to the T allele. Further experiments revealed that 72-hour cholesterol depletion increases miR-1908-5p expression (2.11-fold) whereas cholesterol loading decreases miR-1908-5p expression (0.69-fold). Differential miR-1908-5p expression was then used to profile genes involved in lipoprotein signaling and cholesterol metabolism using a PCR array to identify LDLR as a gene of interest. Although total RNA and protein expression of LDLR was unchanged in response to differential miR-1908-5p expression, the ratio of the mature form to the cleaved form of LDLR decreased following miR-1908-5p inhibition (0.85-fold) and conversely, increased with mimic treatment (1.63-fold). Cleavage of the mature LDLR is known to reduce cell surface affinity for LDL. These findings uncover a potential mechanism linking miR-1908-5p to lower LDL-cholesterol levels through reduced LDLR cleavage.

Low density lipoprotein receptor (LDLR) is an apolipoprotein E (apoE) receptor and may play a role in Alzheimer’s disease (AD) development. A single nucleotide polymorphism (SNP), rs688, that has been identified to modulate the splicing efficiency of LDLR exon 12 and is associated with higher cholesterol and AD in some case-control populations. The exon 12 deleted mRNA is predicted to produce a soluble form of LDLR that fails to mediate apoE uptake. To gain additional insights, in this study, I seek to understand the regulation of LDLR splicing efficiency. To identify functional cis-elements within LDLR exon 12, I mutated several conserved putative exonic splicing enhancers (ESEs) to neutralize their affinity to serine/arginine-rich (SR) proteins. Transfection of wild type (WT) or mutant LDLR minigenes in HepG2 cells was performed, and splicing efficiency evaluated by quantitative RT-PCR. The results showed that two functional ESEs within exon 12, near rs688, are critical to LDLR splicing. To identify splicing factors that modulate exon 12 splicing, I co-transfected an LDLR minigene and vectors encoding different SR proteins and heterogeneous nuclear ribonucleoproteins (hnRNPs). After quantifying the splicing efficiency, I found that SRp20 and SRp38 increased exon 11- skipping. Moreover, ectopic expression of SRp38-2 and hnRNP G increased exon 11&12-skipping. Interestingly, the actions of hnRNP G did not require its RNA recognition motif (RRM). To further investigate the role of theses splicing factors on LDLR splicing, I quantified the expression level of these splicing factors as well as LDLR splicing efficiency in human brain and liver. I found that SRp38 mRNA expression is associated with LDLR splicing efficiency. In conclusion, this study discovered that rs688 is located close to the two functional ESEs within LDLR exon 12, and revealed a role of SRp38 in LDLR splicing efficiency.

A hipercolesterolemia familial (HF) é uma doença autossômica dominante considerada como uma das formas mais graves de hiperlipidemia, assim como, a principal causa de morbi-mortalidade por ser o principal fator desencadeante da aterosclerose. A alteração primária e mais freqüente da HF incide no gene do receptor da LDL (LDLr), sabe-se que mais de 1600 mutações são descritas na literatura e a principal consequência dessas alterações resultam no comprometimento da remoção da LDL, aumentando a concentração plasmática. Atualmente, o ultrasequenciamento genômico permite gerar muitos dados, que podem identificar novas mutações gênicas de forma eficiente, reprodutiva e rápida. No entanto, somente a validação da nova mutação por atividade funcional pode realmente estabelecer a associação com a doença. O presente estudo tem como objetivo realizar a análise da atividade do receptor da LDL, identificadas através do sequenciamento de alto rendimento, no gene LDLr realizado pelo nosso grupo de pesquisa e correlacionar com dados clínicos, in vitro, in silico e estrutural. Para cumprir esta meta, os linfócitos T dos portadores de HF foram isolados do sangue periférico, cultivados e submetidos a estímulo para a expressão de receptores da LDL, incubados com LDL marcada para avaliação de ligação e interiorização pelas células de cada paciente. Dos 30 pacientes selecionados para esse estudo, 63% apresentaram mutação no LDLR, sendo que quase todas as variantes (p.Gly373Asp, p.Asp601His, p.Ile488Thr, p.Gly549Asp, p.Gly592Glu e Gly681Asp) são localizadas no segundo domínio entre os éxons 7 ao 14. De acordo com o docking molecular a variante p.Gly592Glu (rs137929307), que já foi identificada na população polonesa, espanhola e brasileira, já relacionada com a HF, pode aumentar a interação do LDLr com a ApoB e consequentemente o modo de interação entre as proteínas, no estudo in vitro foi possível notar um aumento tanto na média de fluorescência da ligação e da ligação e interiorização em relação a quantidade de LDLr na superfície celular. / Familial hypercholesterolemia (HF) is an autosomal dominant disease considered as one of the most severe forms of hyperlipidemia, as well as the main cause of morbidity and mortality because it is the main triggering factor for atherosclerosis. The primary and more frequent alteration of the HF affects the LDL receptor gene (LDLr), it is known that more than 1600 mutations are described in the literature and the main consequence of these alterations results in the compromise of the LDL removal, increasing the plasma concentration. Nowadays, genomic ultrasequencing allows the generation of many data, which can identify new gene mutations efficiently, reproductively and rapidly. However, only the validation of the new functional activity mutation can actually establish association with the disease. The aim of the present study was to analyze LDL receptor activity, identified by high-throughput sequencing, in the LDLr gene performed by our research group and to correlate with clinical, in vitro, in silico and structural data. To meet this goal, the T lymphocytes from the HF carriers were isolated from the peripheral blood, cultured and challenged for the expression of LDL receptors, incubated with labeled LDL for binding assessment and internalization by the cells of each patient. Of the 30 patients selected for this study, 63% had a mutation in LDLR, and almost all variants (p.Gly373Asp, p.Asp601His, p.Ile488Thr, p.Gly549Asp, p.Gly592Glu and Gly681Asp) are located in the second domain between exons 7 to 14. According to the molecular docking the variant p.Gly592Glu (rs137929307), which has already been identified in the Polish, Spanish and Brazilian population, already related to HF, can increase the interaction of LDLr with ApoB and consequently the mode of interaction between proteins, in the in vitro study it was possible to note an increase in both the mean fluorescence of binding and binding and internalization in relation to the amount of LDLr on the cell surface.

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.

Hipercolesterolemia familiar (HF) é uma doença autossômica dominante, caracterizada por elevados níveis plasmáticos da lipoproteína de baixa densidade (LDL), desenvolvimento de xantoma tendíneo e arco corneal, além do aumento do risco de doença coronariana e acidente vascular cerebral prematuros. Frequentemente subdiagnosticada, estima-se que apenas 10% dos 400.000 indivíduos com HF no Brasil têm conhecimento da própria doença; afetando, desta forma, a qualidade e a expetativa de vida dos pacientes. Mutações no gene do receptor da LDL (LDLR) são consideradas as alterações genéticas mais frequentes para o desenvolvimento da hipercolesterolemia familiar, pois comprometem a capacidade de remoção das partículas de LDL circulantes, promovendo seu aumento em níveis plasmáticos. Já foram descritas mais de 1600 mutações diferentes no gene LDLR associadas ao fenótipo da HF; entretanto, ainda é difícil determinar em muitas delas o efeito deletério na atividade do receptor. O objetivo desse estudo foi identificar e caracterizar funcionalmente mutações no gene LDLR não descritas na literatura para determinar sua patogenicidade na hipercolesterolemia familiar. Foi avaliada a atividade residual de LDLR através da captação de LDL marcado com fluoróforo lipofílico em cultura de linfócitos T dos pacientes portadores das mutações analisadas após estimulação dos linfócitos T por mitógenos específicos. As mutações Cys82Ser, Thr404Ser, Gly529Arg e His285Tyr foram consideradas patogênicas por acarretarem diminuição da atividade residual do receptor de LDL. As mutações Glu 602X e His388ProfsX53 confirmaram sua patogenicidade e podem ser considerados como controle positivo para futuros ensaios funcionais. Estudos que esclareçam os mecanismos moleculares da HF e da relação genótipo/fenótipo abrem perspectivas para o desenvolvimento de terapias mais específicas na redução dos níveis de colesterol e, consequentemente, da morbidade e mortalidade associadas às doenças cardiovasculares. / Familial hypercholesterolemia (FH) is an autosomal dominant disorder characterized by elevated plasma levels of low-density lipoprotein (LDL), and development of corneal arcus tendinous xanthoma, and increased risk of coronary heart disease and premature stroke. Often misdiagnosed, it is estimated that only 10% of the 400.000 patients with FH in Brazil has knowledge of the disease itself, affecting in this way the quality and life expectancy of patients. Mutations in the LDL receptor (LDLR) are considered the most frequent genetic alterations for the development of familial hypercholesterolemia because compromise the ability of removal of circulating LDL particles, promoting its increase in plasma levels. Have been described over 1600 different mutations in the LDLR gene associated with the phenotype of FH, however, it is still difficult to determine in many of the deleterious effects on receptor activity. The aim of this study was to identify mutations in the LDLR gene and functionally characterize mutations not described in the literature to determine its pathogenicity in familial hypercholesterolemia. The residual activity of LDLR was evaluated by raising LDL labeled with lipophilic fluorophore in cultured T lymphocytes of patients with the analyzed mutations after stimulation of T lymphocytes by specific mitogen. The substitution mutations Cys82Ser, Thr404Ser, Gly529Arg e His285Tyr were considered pathogenic because it causes decrease of the residual activity of the LDL receptor in T lymphocytes. The His388ProfsX53 and Glu602X mutations confirmed their pathogenicity and can be considered as positive control for future functional assays. Studies to clarify the molecular mechanisms of HF and genotype/ phenotype open perspectives for the development of more specific therapies for reducing cholesterol levels, and therefore the morbidity and mortality associated with cardiovascular diseases.

A hipercolesterolemia familiar (HF) é uma doença autossômica dominante causada por mutações no gene do receptor de LDL (LDLR) (cromossomo 19p13.1 - p13.3), que alteram parcialmente ou totalmente a função do LDLR. A HF é também uma das doenças genéticas mais comuns com freqüências estimadas de heterozigotos e homozigotos de 1/500 e 1/1.000.000, respectivamente. Manifesta-se com altos níveis de LDL colesterol, arco corneal, xantomas tendíneos e sintomas prematuros de doença coronariana.. A grande heterogeneidade observada na manifestação clínica desta doença pode ser explicada, ao menos parcialmente, pelo amplo espectro de mutações no gene do LDLR. O presente estudo teve por objetivo a caracterização molecular do gene LDLR em pacientes com HF do Rio Grande do Sul (RS), Brasil. Para isso, foram obtidas amostras de DNA de 40 indivíduos provenientes de cinco macrorregiões do Estado, representando seis diferentes populações de ascendência européia, para a realização do seqüenciamento direto do gene do LDLR, com posterior análise por meio das ferramentas de bioinformática. Quinze mutações pontuais foram identificadas no gene do LDLR, a saber: c.408C>T (D115D), c.1616C>T (P518L), c.1773C>T (N570N) e c.2243A>G (D727G) na região codificadora, IVS6+36G>A, IVS6+171G>A, IVS11+56C>T, IVS11- 69G>T, IVS11-55A>C, IVS15-136A>G, IVS16+46C>T e IVS17-42A>G na região intrônica, e *52G>A, *105T>G e *141G>A na região 3\'-UTR. Destas, oito ainda não foram descritas na literatura (três situadas nos exons, quatro nos introns e uma na região 3\'-UTR). A mutação*52G>A foi previamente identificada em pacientes com HF da região Sudeste do Brasil, sugerindo que possa exercer um importante efeito na patogênese da HF em pacientes brasileiros. Em relação às macrorregiões do RS, os portugueses, italianos e espanhóis apresentaram o maior número de mutações dentre os grupos étnicos analisados. Assim, os resultados obtidos confirmam que existe um amplo de espectro de mutações no gene do LDLR. As mutações nas regiões intrônicas precisam ser investigadas sobre seu efeito potencial no desenvolvimento de HF. Considerando que este é o primeiro estudo que teve por objetivo a caracterização molecular de pacientes com HF no RS, novos estudos que visem a elucidação das bases moleculares da HF devem ser realizados, a fim de obter uma melhor caracterização genética desta doença no Brasil. / Familial hypercholesterolemia (FH) is an autosomal dominant disorder caused by mutations in the low-density lipoprotein receptor (LDLR) gene (chromosome 19p13.1 - p13.3), which alter partially or totally the LDLR function. FH is also one of the most common inherited disorders with frequencies of heterozygotes and homozygotes estimated to be 1/500 and 1/1.000.000, respectively. Affected individuals display high levels of LDL cholesterol, arcus corneae, tendon xanthomas and premature symptomatic coronary heart disease. The extensive heterogeneity observed in the clinical manifestation of this disorder may be explained, at least partially, by the broad spectrum of mutations identified in the LDLR gene. The present study had as the main goal the molecular characterization of the LDLR gene in patients with FH from Rio Grande do Sul (RS) State, Brazil. For this, DNA samples were obtained from 40 individuals living in five macroregions of RS, representing six different isolated populations of European ascendancy. The LDLR gene was subjected to the direct sequencing with further analysis through bioinformatics tools. Fifteen punctual mutations were identified in the LDLR gene, namely: c.408C>T (D115D), c.1616C>T (P518L), c.1773C>T (N570N) and c.2243A>G (D727G) in the coding region, IVS6+36G>A, IVS6+171G>A, IVS11+56C>T, IVS11-69G>T, IVS11-55A>C, IVS15-136A>G, IVS16+46C>T and IVS17-42A>G in the intronic region, and *52G>A, *105T>G and *141G>A in the 3\'-UTR region. Of these, eight were not yet described in the literature (three situated in exons, four in introns and one in 3\'- UTR region). The *52G>A mutation was previously identified in FH patients from Southeast Brazil, suggesting that it can exert an important effect in the pathogenesis of FH in Brazilian patients. In relation to the macroregions of Rio Grande do Sul, Portuguese, Italian and Spanish subjects carried the highest number of mutations among the ethnic groups analyzed. Thus, the results obtained confirm the existence of a broad spectrum of mutations in the LDLR gene. The mutations in intronic regions need to be investigated in relation to its potential effect in the development of FH. Taking into account that this is the first study that had as the goal the molecular characterization of FH patients in RS, further studies aimed at elucidating the molecular bases of FH should be performed, in order to obtain the better characterization of this disease in Brazil.

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.

A hipercolesterolemia familiar (HF) é uma doença autossômica dominante causada por mutações no gene do receptor de LDL (LDLR) (cromossomo 19p13.1 - p13.3), que alteram parcialmente ou totalmente a função do LDLR. A HF é também uma das doenças genéticas mais comuns com freqüências estimadas de heterozigotos e homozigotos de 1/500 e 1/1.000.000, respectivamente. Manifesta-se com altos níveis de LDL colesterol, arco corneal, xantomas tendíneos e sintomas prematuros de doença coronariana.. A grande heterogeneidade observada na manifestação clínica desta doença pode ser explicada, ao menos parcialmente, pelo amplo espectro de mutações no gene do LDLR. O presente estudo teve por objetivo a caracterização molecular do gene LDLR em pacientes com HF do Rio Grande do Sul (RS), Brasil. Para isso, foram obtidas amostras de DNA de 40 indivíduos provenientes de cinco macrorregiões do Estado, representando seis diferentes populações de ascendência européia, para a realização do seqüenciamento direto do gene do LDLR, com posterior análise por meio das ferramentas de bioinformática. Quinze mutações pontuais foram identificadas no gene do LDLR, a saber: c.408C>T (D115D), c.1616C>T (P518L), c.1773C>T (N570N) e c.2243A>G (D727G) na região codificadora, IVS6+36G>A, IVS6+171G>A, IVS11+56C>T, IVS11- 69G>T, IVS11-55A>C, IVS15-136A>G, IVS16+46C>T e IVS17-42A>G na região intrônica, e *52G>A, *105T>G e *141G>A na região 3\'-UTR. Destas, oito ainda não foram descritas na literatura (três situadas nos exons, quatro nos introns e uma na região 3\'-UTR). A mutação*52G>A foi previamente identificada em pacientes com HF da região Sudeste do Brasil, sugerindo que possa exercer um importante efeito na patogênese da HF em pacientes brasileiros. Em relação às macrorregiões do RS, os portugueses, italianos e espanhóis apresentaram o maior número de mutações dentre os grupos étnicos analisados. Assim, os resultados obtidos confirmam que existe um amplo de espectro de mutações no gene do LDLR. As mutações nas regiões intrônicas precisam ser investigadas sobre seu efeito potencial no desenvolvimento de HF. Considerando que este é o primeiro estudo que teve por objetivo a caracterização molecular de pacientes com HF no RS, novos estudos que visem a elucidação das bases moleculares da HF devem ser realizados, a fim de obter uma melhor caracterização genética desta doença no Brasil. / Familial hypercholesterolemia (FH) is an autosomal dominant disorder caused by mutations in the low-density lipoprotein receptor (LDLR) gene (chromosome 19p13.1 - p13.3), which alter partially or totally the LDLR function. FH is also one of the most common inherited disorders with frequencies of heterozygotes and homozygotes estimated to be 1/500 and 1/1.000.000, respectively. Affected individuals display high levels of LDL cholesterol, arcus corneae, tendon xanthomas and premature symptomatic coronary heart disease. The extensive heterogeneity observed in the clinical manifestation of this disorder may be explained, at least partially, by the broad spectrum of mutations identified in the LDLR gene. The present study had as the main goal the molecular characterization of the LDLR gene in patients with FH from Rio Grande do Sul (RS) State, Brazil. For this, DNA samples were obtained from 40 individuals living in five macroregions of RS, representing six different isolated populations of European ascendancy. The LDLR gene was subjected to the direct sequencing with further analysis through bioinformatics tools. Fifteen punctual mutations were identified in the LDLR gene, namely: c.408C>T (D115D), c.1616C>T (P518L), c.1773C>T (N570N) and c.2243A>G (D727G) in the coding region, IVS6+36G>A, IVS6+171G>A, IVS11+56C>T, IVS11-69G>T, IVS11-55A>C, IVS15-136A>G, IVS16+46C>T and IVS17-42A>G in the intronic region, and *52G>A, *105T>G and *141G>A in the 3\'-UTR region. Of these, eight were not yet described in the literature (three situated in exons, four in introns and one in 3\'- UTR region). The *52G>A mutation was previously identified in FH patients from Southeast Brazil, suggesting that it can exert an important effect in the pathogenesis of FH in Brazilian patients. In relation to the macroregions of Rio Grande do Sul, Portuguese, Italian and Spanish subjects carried the highest number of mutations among the ethnic groups analyzed. Thus, the results obtained confirm the existence of a broad spectrum of mutations in the LDLR gene. The mutations in intronic regions need to be investigated in relation to its potential effect in the development of FH. Taking into account that this is the first study that had as the goal the molecular characterization of FH patients in RS, further studies aimed at elucidating the molecular bases of FH should be performed, in order to obtain the better characterization of this disease in Brazil.

Hipercolesterolemia familiar (HF) é uma doença autossômica dominante, caracterizada por elevados níveis plasmáticos da lipoproteína de baixa densidade (LDL), desenvolvimento de xantoma tendíneo e arco corneal, além do aumento do risco de doença coronariana e acidente vascular cerebral prematuros. Frequentemente subdiagnosticada, estima-se que apenas 10% dos 400.000 indivíduos com HF no Brasil têm conhecimento da própria doença; afetando, desta forma, a qualidade e a expetativa de vida dos pacientes. Mutações no gene do receptor da LDL (LDLR) são consideradas as alterações genéticas mais frequentes para o desenvolvimento da hipercolesterolemia familiar, pois comprometem a capacidade de remoção das partículas de LDL circulantes, promovendo seu aumento em níveis plasmáticos. Já foram descritas mais de 1600 mutações diferentes no gene LDLR associadas ao fenótipo da HF; entretanto, ainda é difícil determinar em muitas delas o efeito deletério na atividade do receptor. O objetivo desse estudo foi identificar e caracterizar funcionalmente mutações no gene LDLR não descritas na literatura para determinar sua patogenicidade na hipercolesterolemia familiar. Foi avaliada a atividade residual de LDLR através da captação de LDL marcado com fluoróforo lipofílico em cultura de linfócitos T dos pacientes portadores das mutações analisadas após estimulação dos linfócitos T por mitógenos específicos. As mutações Cys82Ser, Thr404Ser, Gly529Arg e His285Tyr foram consideradas patogênicas por acarretarem diminuição da atividade residual do receptor de LDL. As mutações Glu 602X e His388ProfsX53 confirmaram sua patogenicidade e podem ser considerados como controle positivo para futuros ensaios funcionais. Estudos que esclareçam os mecanismos moleculares da HF e da relação genótipo/fenótipo abrem perspectivas para o desenvolvimento de terapias mais específicas na redução dos níveis de colesterol e, consequentemente, da morbidade e mortalidade associadas às doenças cardiovasculares. / Familial hypercholesterolemia (FH) is an autosomal dominant disorder characterized by elevated plasma levels of low-density lipoprotein (LDL), and development of corneal arcus tendinous xanthoma, and increased risk of coronary heart disease and premature stroke. Often misdiagnosed, it is estimated that only 10% of the 400.000 patients with FH in Brazil has knowledge of the disease itself, affecting in this way the quality and life expectancy of patients. Mutations in the LDL receptor (LDLR) are considered the most frequent genetic alterations for the development of familial hypercholesterolemia because compromise the ability of removal of circulating LDL particles, promoting its increase in plasma levels. Have been described over 1600 different mutations in the LDLR gene associated with the phenotype of FH, however, it is still difficult to determine in many of the deleterious effects on receptor activity. The aim of this study was to identify mutations in the LDLR gene and functionally characterize mutations not described in the literature to determine its pathogenicity in familial hypercholesterolemia. The residual activity of LDLR was evaluated by raising LDL labeled with lipophilic fluorophore in cultured T lymphocytes of patients with the analyzed mutations after stimulation of T lymphocytes by specific mitogen. The substitution mutations Cys82Ser, Thr404Ser, Gly529Arg e His285Tyr were considered pathogenic because it causes decrease of the residual activity of the LDL receptor in T lymphocytes. The His388ProfsX53 and Glu602X mutations confirmed their pathogenicity and can be considered as positive control for future functional assays. Studies to clarify the molecular mechanisms of HF and genotype/ phenotype open perspectives for the development of more specific therapies for reducing cholesterol levels, and therefore the morbidity and mortality associated with cardiovascular diseases.

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