Hjärthypertrofi : transkriptionsmönster, hypertrofisk progression och extracellulär signalering

Background: The aim of this thesis was to study transcription patterns and extracellular signalling of the hypertrophic heart to better understand the mechanisms initiating, controlling and maintaining cardiac hypertrophy. Cardiac hypertrophy is a risk factor for cardiovascular morbidity and mortality. Hypertrophy of the myocardium is a state, independent of underlying disease, where the myocardium strives to compensate for an increased workload. This remodelling of the heart includes physiological changes induced by a changed gene expression, alteration of the extracellular matrix and diverse cell-to-cell signalling. Shedding microvesicles and exosomes are membrane released vesicles derived from the plasma membrane, which can mediate messages between cells and induce various cell-related processes in target cells. Methods and materials: Two different microarray studies on different materials were performed. In the first study, cardiac myectomies from 8 patients with hypertrophic obstructive cardiomyopathy (HOCM) and 5 controls without cardiac disease were used. In the second study, myocardial tissue from 6 aorta ligated and 6 sham operated (controls) rats at three different time points (1, 6 and 42 days post-surgically) were analysed. To reveal differences in gene expression the materials were analyzed with Illumina whole genome microarray and multivariate data analysis (PCA and OPLS-DA). Cultured cardiomyocytes (HL-1) were incubated with and without growth factors (TGF-β2 or PDGF BB). Microvesicles and exosomes were collected and isolated after differential centrifugations and ultracentrifugations of the cell culture medium. The microvesicles and exosomes were characterized with dynamic light scattering (DLS), flow cytometry, western blot, electron microscopy and Illumina whole genome microarray. Results: The two different microarray studies revealed differentially expressed gene transcripts and groups of transcripts. When comparing HOCM patients to controls significant down-regulation of the MYH6 gene transcript and two immediate early genes (IEGs, EGR1 and FOS), as well as significant up-regulation of the ACE2, JAK2 and HDAC5 gene transcripts were found. In the rat model, 5 gene groups showed interesting clustering after multivariate data analysis (OPLS-DA) associated with the hypertrophic development: “Atherosclerosis”, “ECM and adhesion molecules”, “Fatty acid metabolism”, “Glucose metabolism” and “Mitochondria”. The shedding microvesicles were rounded vesicles, 40-300 nm in size and surrounded by a bilayered membrane. Chromosomal DNA sequences were identified in the microvesicles. The microvesicles could be taken up by fibroblasts resulting in an altered gene expression in the fibroblasts. The exosomes from cultured cardiomyocytes (incubated with TGF-β2 or PDGF BB) had an average diameter of 50-80 nm, similar to the unstimulated control exosomes. A large, for all cardiomyocyte derived exosomes, common pool of mRNA seems stable and a smaller pool varied in mRNA content according to treatment of the cardiomyocyte. Of the common mRNA about 14% were ribosomal, 14% were of unknown locus and 5% connected to the function of the mitochondria. Conclusions: The microarray studies showed that transcriptional regulation at a stable stage of the hypertrophic development is a balance of pro and anti hypertrophic mechanisms and that diverse gene groups are differently regulated at different time points in the hypertrophic progression. OPLS-DA is a very useful and powerful tool when analyzing gene expression data, especially in finding clusters of gene groups not seen with traditional statistics. The extracellular vesicle studies suggests that microvesicles and exosomes released from cardiomyocytes contain DNA and can be involved in events in target cells by facilitating an array of processes including gene expression changes. Different treatment of the cardiomyocyte influence the content of the exosome produced, indicating that the signal function of the exosome might vary according to the state of the cardiomyocyte.Bakgrund: Syftet med den här avhandlingen var att studera transkriptions-mönster och extracellulär signalering vid hjärthypertrofi för att bättre förstå de mekanismer som startar, styr och underhåller tillväxten. Hjärthypertrofi, onormal tillväxt av hjärtmuskeln, är en riskfaktor för andra hjärt-kärlsjukdomar och dödlighet. Hypertrofi av hjärtmuskeln är ett tillstånd, oberoende av bakomliggande sjukdom, där hjärtmuskeln strävar efter att kompensera för ökad arbetsbelastning. Denna omställning av hjärtat innefattar fysiologiska förändringar orsakade av ett förändrat genuttryck, modifiering av miljön utanför cellen och ändrad cell-till-cell signalering. Mikrovesiklar och exosomer är små membranomslutna bubblor som frisätts från cellmembranet, ut i cellens omgivning. De kan förmedla budskap mellan celler och påverka olika processer i målceller. Metoder och material: Avhandlingen innefattar två olika microarraystudier på olika material. I den första studien användes hjärtbiopsier från 8 patienter med hypertrofisk obstruktiv kardiomyopati (HOCM) och 5 kontroller utan hjärtsjukdom. I det andra projektet användes hjärtvävnad från 6 aortaligerade och 6 skenopererade (kontroller) råttor vid tre olika tidpunkter (1, 6 och 42 dagar efter kirurgiskt ingrepp). För att påvisa skillnader i genuttryck analyserades proverna med Illumina helgenom microarray och multivariat dataanalys. Avhandlingens andra del innehåller två studier om mikrovesiklar och exosomer. Odlade hjärtmuskelceller (HL-1) stimulerades med tillväxt-faktorer (TGF-β2 eller PDGF BB) och ostimulerade celler användes som kontroll. Mikrovesiklar och exosomer renades fram med centrifugeringar och ultracentrifugering av cellodlingsmediet för att sedan karakteriseras med olika metoder för att studera storlek, ytmarkörer och innehåll. Illumina helgenom microarray användes för att studera microvesiklarnas och exosomernas mRNA innehåll. Resultat: I de två olika microarraystudierna hittades gentranskript och grupper av gentranskript som skiljde sig mellan kontroller och den hypertrofa hjärtvävnaden. När HOCM patientproverna jämfördes med kontroller hittades nedreglering av MYH6, EGR1 och FOS samt uppreglering av ACE2, JAK2 och HDAC5. Efter multivariat dataanalys av materialet från råtta, hittades 5 grupper av gentranskript med intressanta mönster som kunde kopplas till den hypertrofiska utvecklingen av hjärtmuskeln: "Ateroskleros", "ECM och adhesionsmolekyler", "Fettsyrametabolism", "Glukosmetabolis-men" och "Mitokondrien". Mikrovesiklarna hade en diameter på 40-300 nm och innehöll kromosomala DNA-sekvenser. När mikrovesiklarna överfördes till en annan celltyp (fibroblaster) resulterade det i ett förändrat genuttryck i fibroblasterna. Exosomer från hjärtmuskelcellerna som odlats med eller utan tillväxtfaktor hade en diameter på 50-80 nm. En stor pool av olika gentranskript var gemensam för alla exosomer oavsett stimulering eller ej. En mindre pool av gentranskript varierade i innehåll mellan de stimulerade och ostimulerade hjärtmuskelcellerna. I den gemensamma gentranskript poolen var ca 14 % ribosomala, ca 14 % var okända och ca 5 % var associerade till mitokondrien och dess funktion. Slutsats: Microarraystudierna visade att transkriptionsreglering i ett stabilt skede av hypertrofiutvecklingen är en balans mellan pro- och anti-hypertrofiska mekanismer och att olika gengrupper var olika reglerade vid olika tidpunkter i hjärtmuskeltillväxten. OPLS-DA är ett mycket användbart och kraftfullt verktyg när man analyserar genexpressionsdata, särskilt för att hitta grupper av gen-transkript som är svåra att upptäcka med traditionell statistik. Microvesikel- och exosomstudierna visade att mikrovesiklar och exosomer som frisätts från hjärtmuskelceller innehåller både DNA och RNA och kan vara inblandade i händelserna i målceller genom att underlätta en rad processer, inklusive ändringar av genuttryck. Olika stimulering av hjärtmuskelcellen kan påverka innehållet i exosomernas som produceras, vilket indikerar att exosomernas signalfunktion kan variera beroende på hjärtmuskelcellens tillstånd

Confocal microscopy images of fibroblasts incubated with microvesicles/exosomes stained with acridine orange.

<p>Confocal microscopy picture of DNA-stained microvesicles/exosomes after dialysis, ultracentrifugation and resuspension in DMEM. After incubation with fibroblasts for 3 h at 37°C the DNA-staining localizes in fibroblasts to and inside the nuclear membrane. Additional light microscopy was used to add a layer in images to visualize cell borders. Arrows in A) and B) indicate acridine orange staining inside nuclei. B) also visualizes red wave length which detects acridine orange staining for RNA. Yellow staining shows colocalization of DNA and RNA.</p

Transcriptional regulation of cardiac genes balance pro- and anti-hypertrophic mechanisms in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is characterized by unexplained left ventricular hypertrophy. HCM is often hereditary, but our knowledge of the mechanisms leading from mutation to phenotype is incomplete. The transcriptional expression patterns in the myocar - dium of HCM patients may contribute to understanding the mechanisms that drive and stabilize the hypertrophy. Cardiac myectomies/biopsies from 8 patients with hypertrophic obstructive cardiomyopathy (HOCM) and 5 controls were studied with whole genome Illumina microarray gene expression (detecting 18 189 mRNA). When comparing HOCM myocardium to controls, there was significant transcriptional down-regulation of the MYH6, EGR1, APOB and FOS genes, and significant transcriptional up-regulation of the ACE2, JAK2, NPPA (ANP), APOA1 and HDAC5 genes. The transcriptional regulation revealed both pro- and anti-hypertrophic mechanisms. The pro-hypertrophic response was explained by the transcriptional down-regulation of MYH6, indicating that the switch to the fetal gene program is maintained, and the transcriptional up-regulation of JAK2 in the JAK-STAT pathway. The anti-hypertrophic response was seen as a transcriptional down-regulation of the immediate early genes (IEGs), FOS and EGR1, and a transcriptional up-regulation of ACE2 and HDAC5. This can be interpreted as a transcriptional endogenous protection system in the heart of the HOCM patients, neither growing nor suppressing the already hypertrophic myocardium

Transmission electron microscopy of purified microvesicles/exosomes.

<p>A) Microvesicles/exosomes displaying an electron dense appearance, and B) electron lucent appearance. Bar represents 100 nm.</p

Filtering of differentially expressed genes.

<p>Fibroblasts incubated for 48 h with Claycomb medium, previously incubated for 24 h with cardiomyocytes were compared to fibroblasts incubated with fresh Claycomb medium.</p><p>Fibroblasts incubated for 48 h with supernatant from ultracentrifuged Claycomb medium, previously incubated for 24 h with cardiomyocytes were compared to fibroblasts incubated with fresh Claycomb medium.</p><p>Fibroblasts incubated for 48 h with pellet from ultracentrifuged Claycomb medium, previously incubated for 48 h with cardiomyocytes. Pellet was dissolved in DMEM and compared to fibroblasts incubated with fresh DMEM.</p><p>False Discovery Rate (FDR) was used for corrections for multiple testing. Significant up-regulation was defined as a foldchange >1.5 and significant down-regulation was defined as foldchange <0.67. A minimum signal intensity value of 50 was utilized. Abbreviations: Cm, cardiomyocytes; Fb, fibroblasts; sup. supernatant after ultracentrifugation; Avg. sign., average signal; FDR, False Discovery Rate; ↑, up-regulated; ↓, down-regulated; DMEM, Dulbecco's modified Eagle's medium.</p

Flow cytometry of DNA-stained microvesicles/exosomes.

<p>A) Enhanced fluorescence at the 530±15 nm channel of membrane permeable acridine orange-stained microvesicles/exosomes (below) in comparison with unstained microvesicles/exosomes (above). B) Weak or no fluorescence at 670 nm/LP channel of membrane impermeable propidium iodide-stained microvesicles/exosomes (below) not differing from unstained microvesicles/exosomes (above).</p

Detection of proteins on microvesicle/exosome surface with flow cytometry.

<p>Microvesicles/exosomes prepared from Claycomb culture medium was incubated with antibodies conjugated with phycoerythrin (PE). A) Mouse anti-caveolin-3, was detected on approximately 30% of the microvesicles/exosomes. B) Mouse anti-flotillin-1, was detected on approximately 80% of the microvesicles/exosomes. C) Mouse anti-annexin-2, was not detected on the microvesicles/exosomes. D) Mouse anti-clathrin heavy chain, was not detected on the microvesicles/exosomes. The distribution of exosomes presenting caveolin-3 and flotillin-1 indicates that the sample contains more than one population of microvesicles/exosomes.</p

Cardiomyocyte microvesicles contain DNA/RNA and convey biological messages to target cells

Background: Shedding microvesicles are membrane released vesicles derived directly from the plasma membrane. Exosomes are released membrane vesicles of late endosomal origin that share structural and biochemical characteristics with prostasomes. Microvesicles/exosomes can mediate messages between cells and affect various cell-related processes in their target cells. We describe newly detected microvesicles/exosomes from cardiomyocytes and depict some of their biological functions. Methodology/Principal Findings: Microvesicles/exosomes from media of cultured cardiomyocytes derived from adult mouse heart were isolated by differential centrifugation including preparative ultracentrifugation and identified by transmission electron microscopy and flow cytometry. They were surrounded by a bilayered membrane and flow cytometry revealed presence of both caveolin-3 and flotillin-1 while clathrin and annexin-2 were not detected. Microvesicle/exosome mRNA was identified and out of 1520 detected mRNA, 423 could be directly connected in a biological network. Furthermore, by a specific technique involving TDT polymerase, 343 different chromosomal DNA sequences were identified in the microvesicles/exosomes. Microvesicle/exosomal DNA transfer was possible into target fibroblasts, where exosomes stained for DNA were seen in the fibroblast cytosol and even in the nuclei. The gene expression was affected in fibroblasts transfected by microvesicles/exosomes and among 333 gene expression changes there were 175 upregulations and 158 downregulations compared with controls. Conclusions/Significance: Our study suggests that microvesicles/exosomes released from cardiomyocytes, where we propose that exosomes derived from cardiomyocytes could be denoted "cardiosomes", can be involved in a metabolic course of events in target cells by facilitating an array of metabolism-related processes including gene expression changes